Date: 2025-03-29T05:58:40+00:00

Actual source code: snes.c

      1: #include <petsc/private/snesimpl.h>
      2: #include <petscdmshell.h>
      3: #include <petscdraw.h>
      4: #include <petscds.h>
      5: #include <petscdmadaptor.h>
      6: #include <petscconvest.h>

      8: PetscBool         SNESRegisterAllCalled = PETSC_FALSE;
      9: PetscFunctionList SNESList              = NULL;

     11: /* Logging support */
     12: PetscClassId  SNES_CLASSID, DMSNES_CLASSID;
     13: PetscLogEvent SNES_Solve, SNES_SetUp, SNES_FunctionEval, SNES_JacobianEval, SNES_NGSEval, SNES_NGSFuncEval, SNES_NewtonALEval, SNES_NPCSolve, SNES_ObjectiveEval;

     15: /*@
     16:   SNESSetErrorIfNotConverged - Causes `SNESSolve()` to generate an error immediately if the solver has not converged.

     18:   Logically Collective

     20:   Input Parameters:
     21: + snes - iterative context obtained from `SNESCreate()`
     22: - flg  - `PETSC_TRUE` indicates you want the error generated

     24:   Options Database Key:
     25: . -snes_error_if_not_converged <true,false> - cause an immediate error condition and stop the program if the solver does not converge

     27:   Level: intermediate

     29:   Note:
     30:   Normally PETSc continues if a solver fails to converge, you can call `SNESGetConvergedReason()` after a `SNESSolve()`
     31:   to determine if it has converged. Otherwise the solution may be inaccurate or wrong

     33: .seealso: [](ch_snes), `SNES`, `SNESGetErrorIfNotConverged()`, `KSPGetErrorIfNotConverged()`, `KSPSetErrorIfNotConverged()`
     34: @*/
     35: PetscErrorCode SNESSetErrorIfNotConverged(SNES snes, PetscBool flg)
     36: {
     37:   PetscFunctionBegin;
     40:   snes->errorifnotconverged = flg;
     41:   PetscFunctionReturn(PETSC_SUCCESS);
     42: }

     44: /*@
     45:   SNESGetErrorIfNotConverged - Indicates if `SNESSolve()` will generate an error if the solver does not converge?

     47:   Not Collective

     49:   Input Parameter:
     50: . snes - iterative context obtained from `SNESCreate()`

     52:   Output Parameter:
     53: . flag - `PETSC_TRUE` if it will generate an error, else `PETSC_FALSE`

     55:   Level: intermediate

     57: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetErrorIfNotConverged()`, `KSPGetErrorIfNotConverged()`, `KSPSetErrorIfNotConverged()`
     58: @*/
     59: PetscErrorCode SNESGetErrorIfNotConverged(SNES snes, PetscBool *flag)
     60: {
     61:   PetscFunctionBegin;
     63:   PetscAssertPointer(flag, 2);
     64:   *flag = snes->errorifnotconverged;
     65:   PetscFunctionReturn(PETSC_SUCCESS);
     66: }

     68: /*@
     69:   SNESSetAlwaysComputesFinalResidual - tells the `SNES` to always compute the residual (nonlinear function value) at the final solution

     71:   Logically Collective

     73:   Input Parameters:
     74: + snes - the shell `SNES`
     75: - flg  - `PETSC_TRUE` to always compute the residual

     77:   Level: advanced

     79:   Note:
     80:   Some solvers (such as smoothers in a `SNESFAS`) do not need the residual computed at the final solution so skip computing it
     81:   to save time.

     83: .seealso: [](ch_snes), `SNES`, `SNESFAS`, `SNESSolve()`, `SNESGetAlwaysComputesFinalResidual()`
     84: @*/
     85: PetscErrorCode SNESSetAlwaysComputesFinalResidual(SNES snes, PetscBool flg)
     86: {
     87:   PetscFunctionBegin;
     89:   snes->alwayscomputesfinalresidual = flg;
     90:   PetscFunctionReturn(PETSC_SUCCESS);
     91: }

     93: /*@
     94:   SNESGetAlwaysComputesFinalResidual - checks if the `SNES` always computes the residual at the final solution

     96:   Logically Collective

     98:   Input Parameter:
     99: . snes - the `SNES` context

    101:   Output Parameter:
    102: . flg - `PETSC_TRUE` if the residual is computed

    104:   Level: advanced

    106: .seealso: [](ch_snes), `SNES`, `SNESFAS`, `SNESSolve()`, `SNESSetAlwaysComputesFinalResidual()`
    107: @*/
    108: PetscErrorCode SNESGetAlwaysComputesFinalResidual(SNES snes, PetscBool *flg)
    109: {
    110:   PetscFunctionBegin;
    112:   *flg = snes->alwayscomputesfinalresidual;
    113:   PetscFunctionReturn(PETSC_SUCCESS);
    114: }

    116: /*@
    117:   SNESSetFunctionDomainError - tells `SNES` that the input vector, a proposed new solution, to your function you provided to `SNESSetFunction()` is not
    118:   in the functions domain. For example, a step with negative pressure.

    120:   Logically Collective

    122:   Input Parameter:
    123: . snes - the `SNES` context

    125:   Level: advanced

    127:   Notes:
    128:   If this is called the `SNESSolve()` stops iterating and returns with a `SNESConvergedReason` of `SNES_DIVERGED_FUNCTION_DOMAIN`

    130:   You should always call `SNESGetConvergedReason()` after each `SNESSolve()` and verify if the iteration converged (positive result) or diverged (negative result).

    132:   You can direct `SNES` to avoid certain steps by using `SNESVISetVariableBounds()`, `SNESVISetComputeVariableBounds()` or
    133:   `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`

    135: .seealso: [](ch_snes), `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetJacobianDomainError()`, `SNESVISetVariableBounds()`,
    136:           `SNESVISetComputeVariableBounds()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESConvergedReason`, `SNESGetConvergedReason()`
    137: @*/
    138: PetscErrorCode SNESSetFunctionDomainError(SNES snes)
    139: {
    140:   PetscFunctionBegin;
    142:   PetscCheck(!snes->errorifnotconverged, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "User code indicates input vector is not in the function domain");
    143:   snes->domainerror = PETSC_TRUE;
    144:   PetscFunctionReturn(PETSC_SUCCESS);
    145: }

    147: /*@
    148:   SNESSetJacobianDomainError - tells `SNES` that the function you provided to `SNESSetJacobian()` at the proposed step. For example there is a negative element transformation.

    150:   Logically Collective

    152:   Input Parameter:
    153: . snes - the `SNES` context

    155:   Level: advanced

    157:   Notes:
    158:   If this is called the `SNESSolve()` stops iterating and returns with a `SNESConvergedReason` of `SNES_DIVERGED_FUNCTION_DOMAIN`

    160:   You should always call `SNESGetConvergedReason()` after each `SNESSolve()` and verify if the iteration converged (positive result) or diverged (negative result).

    162:   You can direct `SNES` to avoid certain steps by using `SNESVISetVariableBounds()`, `SNESVISetComputeVariableBounds()` or
    163:   `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`

    165: .seealso: [](ch_snes), `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetFunctionDomainError()`, `SNESVISetVariableBounds()`,
    166:           `SNESVISetComputeVariableBounds()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESConvergedReason`, `SNESGetConvergedReason()`
    167: @*/
    168: PetscErrorCode SNESSetJacobianDomainError(SNES snes)
    169: {
    170:   PetscFunctionBegin;
    172:   PetscCheck(!snes->errorifnotconverged, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "User code indicates computeJacobian does not make sense");
    173:   snes->jacobiandomainerror = PETSC_TRUE;
    174:   PetscFunctionReturn(PETSC_SUCCESS);
    175: }

    177: /*@
    178:   SNESSetCheckJacobianDomainError - tells `SNESSolve()` whether to check if the user called `SNESSetJacobianDomainError()` Jacobian domain error after
    179:   each Jacobian evaluation. By default, it checks for the Jacobian domain error in the debug mode, and does not check it in the optimized mode.

    181:   Logically Collective

    183:   Input Parameters:
    184: + snes - the `SNES` context
    185: - flg  - indicates if or not to check Jacobian domain error after each Jacobian evaluation

    187:   Level: advanced

    189:   Note:
    190:   Checks require one extra parallel synchronization for each Jacobian evaluation

    192: .seealso: [](ch_snes), `SNES`, `SNESConvergedReason`, `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetFunctionDomainError()`, `SNESGetCheckJacobianDomainError()`
    193: @*/
    194: PetscErrorCode SNESSetCheckJacobianDomainError(SNES snes, PetscBool flg)
    195: {
    196:   PetscFunctionBegin;
    198:   snes->checkjacdomainerror = flg;
    199:   PetscFunctionReturn(PETSC_SUCCESS);
    200: }

    202: /*@
    203:   SNESGetCheckJacobianDomainError - Get an indicator whether or not `SNES` is checking Jacobian domain errors after each Jacobian evaluation.

    205:   Logically Collective

    207:   Input Parameter:
    208: . snes - the `SNES` context

    210:   Output Parameter:
    211: . flg - `PETSC_FALSE` indicates that it is not checking Jacobian domain errors after each Jacobian evaluation

    213:   Level: advanced

    215: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetFunctionDomainError()`, `SNESSetCheckJacobianDomainError()`
    216: @*/
    217: PetscErrorCode SNESGetCheckJacobianDomainError(SNES snes, PetscBool *flg)
    218: {
    219:   PetscFunctionBegin;
    221:   PetscAssertPointer(flg, 2);
    222:   *flg = snes->checkjacdomainerror;
    223:   PetscFunctionReturn(PETSC_SUCCESS);
    224: }

    226: /*@
    227:   SNESGetFunctionDomainError - Gets the status of the domain error after a call to `SNESComputeFunction()`

    229:   Logically Collective

    231:   Input Parameter:
    232: . snes - the `SNES` context

    234:   Output Parameter:
    235: . domainerror - Set to `PETSC_TRUE` if there's a domain error; `PETSC_FALSE` otherwise.

    237:   Level: developer

    239: .seealso: [](ch_snes), `SNES`, `SNESSetFunctionDomainError()`, `SNESComputeFunction()`
    240: @*/
    241: PetscErrorCode SNESGetFunctionDomainError(SNES snes, PetscBool *domainerror)
    242: {
    243:   PetscFunctionBegin;
    245:   PetscAssertPointer(domainerror, 2);
    246:   *domainerror = snes->domainerror;
    247:   PetscFunctionReturn(PETSC_SUCCESS);
    248: }

    250: /*@
    251:   SNESGetJacobianDomainError - Gets the status of the Jacobian domain error after a call to `SNESComputeJacobian()`

    253:   Logically Collective

    255:   Input Parameter:
    256: . snes - the `SNES` context

    258:   Output Parameter:
    259: . domainerror - Set to `PETSC_TRUE` if there's a Jacobian domain error; `PETSC_FALSE` otherwise.

    261:   Level: advanced

    263: .seealso: [](ch_snes), `SNES`, `SNESSetFunctionDomainError()`, `SNESComputeFunction()`, `SNESGetFunctionDomainError()`
    264: @*/
    265: PetscErrorCode SNESGetJacobianDomainError(SNES snes, PetscBool *domainerror)
    266: {
    267:   PetscFunctionBegin;
    269:   PetscAssertPointer(domainerror, 2);
    270:   *domainerror = snes->jacobiandomainerror;
    271:   PetscFunctionReturn(PETSC_SUCCESS);
    272: }

    274: /*@
    275:   SNESLoad - Loads a `SNES` that has been stored in `PETSCVIEWERBINARY` with `SNESView()`.

    277:   Collective

    279:   Input Parameters:
    280: + snes   - the newly loaded `SNES`, this needs to have been created with `SNESCreate()` or
    281:            some related function before a call to `SNESLoad()`.
    282: - viewer - binary file viewer, obtained from `PetscViewerBinaryOpen()`

    284:   Level: intermediate

    286:   Note:
    287:   The `SNESType` is determined by the data in the file, any type set into the `SNES` before this call is ignored.

    289: .seealso: [](ch_snes), `SNES`, `PetscViewer`, `SNESCreate()`, `SNESType`, `PetscViewerBinaryOpen()`, `SNESView()`, `MatLoad()`, `VecLoad()`
    290: @*/
    291: PetscErrorCode SNESLoad(SNES snes, PetscViewer viewer)
    292: {
    293:   PetscBool isbinary;
    294:   PetscInt  classid;
    295:   char      type[256];
    296:   KSP       ksp;
    297:   DM        dm;
    298:   DMSNES    dmsnes;

    300:   PetscFunctionBegin;
    303:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERBINARY, &isbinary));
    304:   PetscCheck(isbinary, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Invalid viewer; open viewer with PetscViewerBinaryOpen()");

    306:   PetscCall(PetscViewerBinaryRead(viewer, &classid, 1, NULL, PETSC_INT));
    307:   PetscCheck(classid == SNES_FILE_CLASSID, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_WRONG, "Not SNES next in file");
    308:   PetscCall(PetscViewerBinaryRead(viewer, type, 256, NULL, PETSC_CHAR));
    309:   PetscCall(SNESSetType(snes, type));
    310:   PetscTryTypeMethod(snes, load, viewer);
    311:   PetscCall(SNESGetDM(snes, &dm));
    312:   PetscCall(DMGetDMSNES(dm, &dmsnes));
    313:   PetscCall(DMSNESLoad(dmsnes, viewer));
    314:   PetscCall(SNESGetKSP(snes, &ksp));
    315:   PetscCall(KSPLoad(ksp, viewer));
    316:   PetscFunctionReturn(PETSC_SUCCESS);
    317: }

    319: #include <petscdraw.h>
    320: #if defined(PETSC_HAVE_SAWS)
    321: #include <petscviewersaws.h>
    322: #endif

    324: /*@
    325:   SNESViewFromOptions - View a `SNES` based on values in the options database

    327:   Collective

    329:   Input Parameters:
    330: + A    - the `SNES` context
    331: . obj  - Optional object that provides the options prefix for the checks
    332: - name - command line option

    334:   Level: intermediate

    336: .seealso: [](ch_snes), `SNES`, `SNESView`, `PetscObjectViewFromOptions()`, `SNESCreate()`
    337: @*/
    338: PetscErrorCode SNESViewFromOptions(SNES A, PetscObject obj, const char name[])
    339: {
    340:   PetscFunctionBegin;
    342:   PetscCall(PetscObjectViewFromOptions((PetscObject)A, obj, name));
    343:   PetscFunctionReturn(PETSC_SUCCESS);
    344: }

    346: PETSC_EXTERN PetscErrorCode SNESComputeJacobian_DMDA(SNES, Vec, Mat, Mat, void *);

    348: /*@
    349:   SNESView - Prints or visualizes the `SNES` data structure.

    351:   Collective

    353:   Input Parameters:
    354: + snes   - the `SNES` context
    355: - viewer - the `PetscViewer`

    357:   Options Database Key:
    358: . -snes_view - Calls `SNESView()` at end of `SNESSolve()`

    360:   Level: beginner

    362:   Notes:
    363:   The available visualization contexts include
    364: +     `PETSC_VIEWER_STDOUT_SELF` - standard output (default)
    365: -     `PETSC_VIEWER_STDOUT_WORLD` - synchronized standard
    366:   output where only the first processor opens
    367:   the file.  All other processors send their
    368:   data to the first processor to print.

    370:   The available formats include
    371: +     `PETSC_VIEWER_DEFAULT` - standard output (default)
    372: -     `PETSC_VIEWER_ASCII_INFO_DETAIL` - more verbose output for `SNESNASM`

    374:   The user can open an alternative visualization context with
    375:   `PetscViewerASCIIOpen()` - output to a specified file.

    377:   In the debugger you can do "call `SNESView`(snes,0)" to display the `SNES` solver. (The same holds for any PETSc object viewer).

    379: .seealso: [](ch_snes), `SNES`, `SNESLoad()`, `SNESCreate()`, `PetscViewerASCIIOpen()`
    380: @*/
    381: PetscErrorCode SNESView(SNES snes, PetscViewer viewer)
    382: {
    383:   SNESKSPEW     *kctx;
    384:   KSP            ksp;
    385:   SNESLineSearch linesearch;
    386:   PetscBool      iascii, isstring, isbinary, isdraw;
    387:   DMSNES         dmsnes;
    388: #if defined(PETSC_HAVE_SAWS)
    389:   PetscBool issaws;
    390: #endif

    392:   PetscFunctionBegin;
    394:   if (!viewer) PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)snes), &viewer));
    396:   PetscCheckSameComm(snes, 1, viewer, 2);

    398:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &iascii));
    399:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERSTRING, &isstring));
    400:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERBINARY, &isbinary));
    401:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERDRAW, &isdraw));
    402: #if defined(PETSC_HAVE_SAWS)
    403:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERSAWS, &issaws));
    404: #endif
    405:   if (iascii) {
    406:     SNESNormSchedule normschedule;
    407:     DM               dm;
    408:     SNESJacobianFn  *cJ;
    409:     void            *ctx;
    410:     const char      *pre = "";

    412:     PetscCall(PetscObjectPrintClassNamePrefixType((PetscObject)snes, viewer));
    413:     if (!snes->setupcalled) PetscCall(PetscViewerASCIIPrintf(viewer, "  SNES has not been set up so information may be incomplete\n"));
    414:     if (snes->ops->view) {
    415:       PetscCall(PetscViewerASCIIPushTab(viewer));
    416:       PetscUseTypeMethod(snes, view, viewer);
    417:       PetscCall(PetscViewerASCIIPopTab(viewer));
    418:     }
    419:     if (snes->max_funcs == PETSC_UNLIMITED) {
    420:       PetscCall(PetscViewerASCIIPrintf(viewer, "  maximum iterations=%" PetscInt_FMT ", maximum function evaluations=unlimited\n", snes->max_its));
    421:     } else {
    422:       PetscCall(PetscViewerASCIIPrintf(viewer, "  maximum iterations=%" PetscInt_FMT ", maximum function evaluations=%" PetscInt_FMT "\n", snes->max_its, snes->max_funcs));
    423:     }
    424:     PetscCall(PetscViewerASCIIPrintf(viewer, "  tolerances: relative=%g, absolute=%g, solution=%g\n", (double)snes->rtol, (double)snes->abstol, (double)snes->stol));
    425:     if (snes->usesksp) PetscCall(PetscViewerASCIIPrintf(viewer, "  total number of linear solver iterations=%" PetscInt_FMT "\n", snes->linear_its));
    426:     PetscCall(PetscViewerASCIIPrintf(viewer, "  total number of function evaluations=%" PetscInt_FMT "\n", snes->nfuncs));
    427:     PetscCall(SNESGetNormSchedule(snes, &normschedule));
    428:     if (normschedule > 0) PetscCall(PetscViewerASCIIPrintf(viewer, "  norm schedule %s\n", SNESNormSchedules[normschedule]));
    429:     if (snes->gridsequence) PetscCall(PetscViewerASCIIPrintf(viewer, "  total number of grid sequence refinements=%" PetscInt_FMT "\n", snes->gridsequence));
    430:     if (snes->ksp_ewconv) {
    431:       kctx = (SNESKSPEW *)snes->kspconvctx;
    432:       if (kctx) {
    433:         PetscCall(PetscViewerASCIIPrintf(viewer, "  Eisenstat-Walker computation of KSP relative tolerance (version %" PetscInt_FMT ")\n", kctx->version));
    434:         PetscCall(PetscViewerASCIIPrintf(viewer, "    rtol_0=%g, rtol_max=%g, threshold=%g\n", (double)kctx->rtol_0, (double)kctx->rtol_max, (double)kctx->threshold));
    435:         PetscCall(PetscViewerASCIIPrintf(viewer, "    gamma=%g, alpha=%g, alpha2=%g\n", (double)kctx->gamma, (double)kctx->alpha, (double)kctx->alpha2));
    436:       }
    437:     }
    438:     if (snes->lagpreconditioner == -1) {
    439:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Preconditioned is never rebuilt\n"));
    440:     } else if (snes->lagpreconditioner > 1) {
    441:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Preconditioned is rebuilt every %" PetscInt_FMT " new Jacobians\n", snes->lagpreconditioner));
    442:     }
    443:     if (snes->lagjacobian == -1) {
    444:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is never rebuilt\n"));
    445:     } else if (snes->lagjacobian > 1) {
    446:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is rebuilt every %" PetscInt_FMT " SNES iterations\n", snes->lagjacobian));
    447:     }
    448:     PetscCall(SNESGetDM(snes, &dm));
    449:     PetscCall(DMSNESGetJacobian(dm, &cJ, &ctx));
    450:     if (snes->mf_operator) {
    451:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is applied matrix-free with differencing\n"));
    452:       pre = "Preconditioning ";
    453:     }
    454:     if (cJ == SNESComputeJacobianDefault) {
    455:       PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using finite differences one column at a time\n", pre));
    456:     } else if (cJ == SNESComputeJacobianDefaultColor) {
    457:       PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using finite differences with coloring\n", pre));
    458:       /* it slightly breaks data encapsulation for access the DMDA information directly */
    459:     } else if (cJ == SNESComputeJacobian_DMDA) {
    460:       MatFDColoring fdcoloring;
    461:       PetscCall(PetscObjectQuery((PetscObject)dm, "DMDASNES_FDCOLORING", (PetscObject *)&fdcoloring));
    462:       if (fdcoloring) {
    463:         PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using colored finite differences on a DMDA\n", pre));
    464:       } else {
    465:         PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using a DMDA local Jacobian\n", pre));
    466:       }
    467:     } else if (snes->mf && !snes->mf_operator) {
    468:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is applied matrix-free with differencing, no explicit Jacobian\n"));
    469:     }
    470:   } else if (isstring) {
    471:     const char *type;
    472:     PetscCall(SNESGetType(snes, &type));
    473:     PetscCall(PetscViewerStringSPrintf(viewer, " SNESType: %-7.7s", type));
    474:     PetscTryTypeMethod(snes, view, viewer);
    475:   } else if (isbinary) {
    476:     PetscInt    classid = SNES_FILE_CLASSID;
    477:     MPI_Comm    comm;
    478:     PetscMPIInt rank;
    479:     char        type[256];

    481:     PetscCall(PetscObjectGetComm((PetscObject)snes, &comm));
    482:     PetscCallMPI(MPI_Comm_rank(comm, &rank));
    483:     if (rank == 0) {
    484:       PetscCall(PetscViewerBinaryWrite(viewer, &classid, 1, PETSC_INT));
    485:       PetscCall(PetscStrncpy(type, ((PetscObject)snes)->type_name, sizeof(type)));
    486:       PetscCall(PetscViewerBinaryWrite(viewer, type, sizeof(type), PETSC_CHAR));
    487:     }
    488:     PetscTryTypeMethod(snes, view, viewer);
    489:   } else if (isdraw) {
    490:     PetscDraw draw;
    491:     char      str[36];
    492:     PetscReal x, y, bottom, h;

    494:     PetscCall(PetscViewerDrawGetDraw(viewer, 0, &draw));
    495:     PetscCall(PetscDrawGetCurrentPoint(draw, &x, &y));
    496:     PetscCall(PetscStrncpy(str, "SNES: ", sizeof(str)));
    497:     PetscCall(PetscStrlcat(str, ((PetscObject)snes)->type_name, sizeof(str)));
    498:     PetscCall(PetscDrawStringBoxed(draw, x, y, PETSC_DRAW_BLUE, PETSC_DRAW_BLACK, str, NULL, &h));
    499:     bottom = y - h;
    500:     PetscCall(PetscDrawPushCurrentPoint(draw, x, bottom));
    501:     PetscTryTypeMethod(snes, view, viewer);
    502: #if defined(PETSC_HAVE_SAWS)
    503:   } else if (issaws) {
    504:     PetscMPIInt rank;
    505:     const char *name;

    507:     PetscCall(PetscObjectGetName((PetscObject)snes, &name));
    508:     PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
    509:     if (!((PetscObject)snes)->amsmem && rank == 0) {
    510:       char dir[1024];

    512:       PetscCall(PetscObjectViewSAWs((PetscObject)snes, viewer));
    513:       PetscCall(PetscSNPrintf(dir, 1024, "/PETSc/Objects/%s/its", name));
    514:       PetscCallSAWs(SAWs_Register, (dir, &snes->iter, 1, SAWs_READ, SAWs_INT));
    515:       if (!snes->conv_hist) PetscCall(SNESSetConvergenceHistory(snes, NULL, NULL, PETSC_DECIDE, PETSC_TRUE));
    516:       PetscCall(PetscSNPrintf(dir, 1024, "/PETSc/Objects/%s/conv_hist", name));
    517:       PetscCallSAWs(SAWs_Register, (dir, snes->conv_hist, 10, SAWs_READ, SAWs_DOUBLE));
    518:     }
    519: #endif
    520:   }
    521:   if (snes->linesearch) {
    522:     PetscCall(SNESGetLineSearch(snes, &linesearch));
    523:     PetscCall(PetscViewerASCIIPushTab(viewer));
    524:     PetscCall(SNESLineSearchView(linesearch, viewer));
    525:     PetscCall(PetscViewerASCIIPopTab(viewer));
    526:   }
    527:   if (snes->npc && snes->usesnpc) {
    528:     PetscCall(PetscViewerASCIIPushTab(viewer));
    529:     PetscCall(SNESView(snes->npc, viewer));
    530:     PetscCall(PetscViewerASCIIPopTab(viewer));
    531:   }
    532:   PetscCall(PetscViewerASCIIPushTab(viewer));
    533:   PetscCall(DMGetDMSNES(snes->dm, &dmsnes));
    534:   PetscCall(DMSNESView(dmsnes, viewer));
    535:   PetscCall(PetscViewerASCIIPopTab(viewer));
    536:   if (snes->usesksp) {
    537:     PetscCall(SNESGetKSP(snes, &ksp));
    538:     PetscCall(PetscViewerASCIIPushTab(viewer));
    539:     PetscCall(KSPView(ksp, viewer));
    540:     PetscCall(PetscViewerASCIIPopTab(viewer));
    541:   }
    542:   if (isdraw) {
    543:     PetscDraw draw;
    544:     PetscCall(PetscViewerDrawGetDraw(viewer, 0, &draw));
    545:     PetscCall(PetscDrawPopCurrentPoint(draw));
    546:   }
    547:   PetscFunctionReturn(PETSC_SUCCESS);
    548: }

    550: /*
    551:   We retain a list of functions that also take SNES command
    552:   line options. These are called at the end SNESSetFromOptions()
    553: */
    554: #define MAXSETFROMOPTIONS 5
    555: static PetscInt numberofsetfromoptions;
    556: static PetscErrorCode (*othersetfromoptions[MAXSETFROMOPTIONS])(SNES);

    558: /*@C
    559:   SNESAddOptionsChecker - Adds an additional function to check for `SNES` options.

    561:   Not Collective

    563:   Input Parameter:
    564: . snescheck - function that checks for options

    566:   Calling sequence of `snescheck`:
    567: . snes - the `SNES` object for which it is checking options

    569:   Level: developer

    571: .seealso: [](ch_snes), `SNES`, `SNESSetFromOptions()`
    572: @*/
    573: PetscErrorCode SNESAddOptionsChecker(PetscErrorCode (*snescheck)(SNES snes))
    574: {
    575:   PetscFunctionBegin;
    576:   PetscCheck(numberofsetfromoptions < MAXSETFROMOPTIONS, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Too many options checkers, only %d allowed", MAXSETFROMOPTIONS);
    577:   othersetfromoptions[numberofsetfromoptions++] = snescheck;
    578:   PetscFunctionReturn(PETSC_SUCCESS);
    579: }

    581: static PetscErrorCode SNESSetUpMatrixFree_Private(SNES snes, PetscBool hasOperator, PetscInt version)
    582: {
    583:   Mat          J;
    584:   MatNullSpace nullsp;

    586:   PetscFunctionBegin;

    589:   if (!snes->vec_func && (snes->jacobian || snes->jacobian_pre)) {
    590:     Mat A = snes->jacobian, B = snes->jacobian_pre;
    591:     PetscCall(MatCreateVecs(A ? A : B, NULL, &snes->vec_func));
    592:   }

    594:   PetscCheck(version == 1 || version == 2, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "matrix-free operator routines, only version 1 and 2");
    595:   if (version == 1) {
    596:     PetscCall(MatCreateSNESMF(snes, &J));
    597:     PetscCall(MatMFFDSetOptionsPrefix(J, ((PetscObject)snes)->prefix));
    598:     PetscCall(MatSetFromOptions(J));
    599:     /* TODO: the version 2 code should be merged into the MatCreateSNESMF() and MatCreateMFFD() infrastructure and then removed */
    600:   } else /* if (version == 2) */ {
    601:     PetscCheck(snes->vec_func, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "SNESSetFunction() must be called first");
    602: #if !defined(PETSC_USE_COMPLEX) && !defined(PETSC_USE_REAL_SINGLE) && !defined(PETSC_USE_REAL___FLOAT128) && !defined(PETSC_USE_REAL___FP16)
    603:     PetscCall(MatCreateSNESMFMore(snes, snes->vec_func, &J));
    604: #else
    605:     SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP, "matrix-free operator routines (version 2)");
    606: #endif
    607:   }

    609:   /* attach any user provided null space that was on Amat to the newly created matrix-free matrix */
    610:   if (snes->jacobian) {
    611:     PetscCall(MatGetNullSpace(snes->jacobian, &nullsp));
    612:     if (nullsp) PetscCall(MatSetNullSpace(J, nullsp));
    613:   }

    615:   PetscCall(PetscInfo(snes, "Setting default matrix-free operator routines (version %" PetscInt_FMT ")\n", version));
    616:   if (hasOperator) {
    617:     /* This version replaces the user provided Jacobian matrix with a
    618:        matrix-free version but still employs the user-provided preconditioner matrix. */
    619:     PetscCall(SNESSetJacobian(snes, J, NULL, NULL, NULL));
    620:   } else {
    621:     /* This version replaces both the user-provided Jacobian and the user-
    622:      provided preconditioner Jacobian with the default matrix-free version. */
    623:     if (snes->npcside == PC_LEFT && snes->npc) {
    624:       if (!snes->jacobian) PetscCall(SNESSetJacobian(snes, J, NULL, NULL, NULL));
    625:     } else {
    626:       KSP       ksp;
    627:       PC        pc;
    628:       PetscBool match;

    630:       PetscCall(SNESSetJacobian(snes, J, J, MatMFFDComputeJacobian, NULL));
    631:       /* Force no preconditioner */
    632:       PetscCall(SNESGetKSP(snes, &ksp));
    633:       PetscCall(KSPGetPC(ksp, &pc));
    634:       PetscCall(PetscObjectTypeCompareAny((PetscObject)pc, &match, PCSHELL, PCH2OPUS, ""));
    635:       if (!match) {
    636:         PetscCall(PetscInfo(snes, "Setting default matrix-free preconditioner routines\nThat is no preconditioner is being used\n"));
    637:         PetscCall(PCSetType(pc, PCNONE));
    638:       }
    639:     }
    640:   }
    641:   PetscCall(MatDestroy(&J));
    642:   PetscFunctionReturn(PETSC_SUCCESS);
    643: }

    645: static PetscErrorCode DMRestrictHook_SNESVecSol(DM dmfine, Mat Restrict, Vec Rscale, Mat Inject, DM dmcoarse, void *ctx)
    646: {
    647:   SNES snes = (SNES)ctx;
    648:   Vec  Xfine, Xfine_named = NULL, Xcoarse;

    650:   PetscFunctionBegin;
    651:   if (PetscLogPrintInfo) {
    652:     PetscInt finelevel, coarselevel, fineclevel, coarseclevel;
    653:     PetscCall(DMGetRefineLevel(dmfine, &finelevel));
    654:     PetscCall(DMGetCoarsenLevel(dmfine, &fineclevel));
    655:     PetscCall(DMGetRefineLevel(dmcoarse, &coarselevel));
    656:     PetscCall(DMGetCoarsenLevel(dmcoarse, &coarseclevel));
    657:     PetscCall(PetscInfo(dmfine, "Restricting SNES solution vector from level %" PetscInt_FMT "-%" PetscInt_FMT " to level %" PetscInt_FMT "-%" PetscInt_FMT "\n", finelevel, fineclevel, coarselevel, coarseclevel));
    658:   }
    659:   if (dmfine == snes->dm) Xfine = snes->vec_sol;
    660:   else {
    661:     PetscCall(DMGetNamedGlobalVector(dmfine, "SNESVecSol", &Xfine_named));
    662:     Xfine = Xfine_named;
    663:   }
    664:   PetscCall(DMGetNamedGlobalVector(dmcoarse, "SNESVecSol", &Xcoarse));
    665:   if (Inject) {
    666:     PetscCall(MatRestrict(Inject, Xfine, Xcoarse));
    667:   } else {
    668:     PetscCall(MatRestrict(Restrict, Xfine, Xcoarse));
    669:     PetscCall(VecPointwiseMult(Xcoarse, Xcoarse, Rscale));
    670:   }
    671:   PetscCall(DMRestoreNamedGlobalVector(dmcoarse, "SNESVecSol", &Xcoarse));
    672:   if (Xfine_named) PetscCall(DMRestoreNamedGlobalVector(dmfine, "SNESVecSol", &Xfine_named));
    673:   PetscFunctionReturn(PETSC_SUCCESS);
    674: }

    676: static PetscErrorCode DMCoarsenHook_SNESVecSol(DM dm, DM dmc, void *ctx)
    677: {
    678:   PetscFunctionBegin;
    679:   PetscCall(DMCoarsenHookAdd(dmc, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, ctx));
    680:   PetscFunctionReturn(PETSC_SUCCESS);
    681: }

    683: /* This may be called to rediscretize the operator on levels of linear multigrid. The DM shuffle is so the user can
    684:  * safely call SNESGetDM() in their residual evaluation routine. */
    685: static PetscErrorCode KSPComputeOperators_SNES(KSP ksp, Mat A, Mat B, void *ctx)
    686: {
    687:   SNES            snes = (SNES)ctx;
    688:   DMSNES          sdm;
    689:   Vec             X, Xnamed = NULL;
    690:   DM              dmsave;
    691:   void           *ctxsave;
    692:   SNESJacobianFn *jac = NULL;

    694:   PetscFunctionBegin;
    695:   dmsave = snes->dm;
    696:   PetscCall(KSPGetDM(ksp, &snes->dm));
    697:   if (dmsave == snes->dm) X = snes->vec_sol; /* We are on the finest level */
    698:   else {
    699:     PetscBool has;

    701:     /* We are on a coarser level, this vec was initialized using a DM restrict hook */
    702:     PetscCall(DMHasNamedGlobalVector(snes->dm, "SNESVecSol", &has));
    703:     PetscCheck(has, PetscObjectComm((PetscObject)snes->dm), PETSC_ERR_PLIB, "Missing SNESVecSol");
    704:     PetscCall(DMGetNamedGlobalVector(snes->dm, "SNESVecSol", &Xnamed));
    705:     X = Xnamed;
    706:     PetscCall(SNESGetJacobian(snes, NULL, NULL, &jac, &ctxsave));
    707:     /* If the DM's don't match up, the MatFDColoring context needed for the jacobian won't match up either -- fixit. */
    708:     if (jac == SNESComputeJacobianDefaultColor) PetscCall(SNESSetJacobian(snes, NULL, NULL, SNESComputeJacobianDefaultColor, NULL));
    709:   }

    711:   /* Compute the operators */
    712:   PetscCall(DMGetDMSNES(snes->dm, &sdm));
    713:   if (Xnamed && sdm->ops->computefunction) {
    714:     /* The SNES contract with the user is that ComputeFunction is always called before ComputeJacobian.
    715:        We make sure of this here. Disable affine shift since it is for the finest level */
    716:     Vec F, saverhs = snes->vec_rhs;

    718:     snes->vec_rhs = NULL;
    719:     PetscCall(DMGetGlobalVector(snes->dm, &F));
    720:     PetscCall(SNESComputeFunction(snes, X, F));
    721:     PetscCall(DMRestoreGlobalVector(snes->dm, &F));
    722:     snes->vec_rhs = saverhs;
    723:     snes->nfuncs--; /* Do not log coarser level evaluations */
    724:   }
    725:   /* Make sure KSP DM has the Jacobian computation routine */
    726:   if (!sdm->ops->computejacobian) PetscCall(DMCopyDMSNES(dmsave, snes->dm));
    727:   PetscCall(SNESComputeJacobian(snes, X, A, B));

    729:   /* Put the previous context back */
    730:   if (snes->dm != dmsave && jac == SNESComputeJacobianDefaultColor) PetscCall(SNESSetJacobian(snes, NULL, NULL, jac, ctxsave));

    732:   if (Xnamed) PetscCall(DMRestoreNamedGlobalVector(snes->dm, "SNESVecSol", &Xnamed));
    733:   snes->dm = dmsave;
    734:   PetscFunctionReturn(PETSC_SUCCESS);
    735: }

    737: /*@
    738:   SNESSetUpMatrices - ensures that matrices are available for `SNES` Newton-like methods, this is called by `SNESSetUp_XXX()`

    740:   Collective

    742:   Input Parameter:
    743: . snes - `SNES` object to configure

    745:   Level: developer

    747:   Note:
    748:   If the matrices do not yet exist it attempts to create them based on options previously set for the `SNES` such as `-snes_mf`

    750:   Developer Note:
    751:   The functionality of this routine overlaps in a confusing way with the functionality of `SNESSetUpMatrixFree_Private()` which is called by
    752:   `SNESSetUp()` but sometimes `SNESSetUpMatrices()` is called without `SNESSetUp()` being called. A refactorization to simplify the
    753:   logic that handles the matrix-free case is desirable.

    755: .seealso: [](ch_snes), `SNES`, `SNESSetUp()`
    756: @*/
    757: PetscErrorCode SNESSetUpMatrices(SNES snes)
    758: {
    759:   DM     dm;
    760:   DMSNES sdm;

    762:   PetscFunctionBegin;
    763:   PetscCall(SNESGetDM(snes, &dm));
    764:   PetscCall(DMGetDMSNES(dm, &sdm));
    765:   if (!snes->jacobian && snes->mf && !snes->mf_operator && !snes->jacobian_pre) {
    766:     Mat   J;
    767:     void *functx;
    768:     PetscCall(MatCreateSNESMF(snes, &J));
    769:     PetscCall(MatMFFDSetOptionsPrefix(J, ((PetscObject)snes)->prefix));
    770:     PetscCall(MatSetFromOptions(J));
    771:     PetscCall(SNESGetFunction(snes, NULL, NULL, &functx));
    772:     PetscCall(SNESSetJacobian(snes, J, J, NULL, NULL));
    773:     PetscCall(MatDestroy(&J));
    774:   } else if (snes->mf_operator && !snes->jacobian_pre && !snes->jacobian) {
    775:     Mat J, B;
    776:     PetscCall(MatCreateSNESMF(snes, &J));
    777:     PetscCall(MatMFFDSetOptionsPrefix(J, ((PetscObject)snes)->prefix));
    778:     PetscCall(MatSetFromOptions(J));
    779:     PetscCall(DMCreateMatrix(snes->dm, &B));
    780:     /* sdm->computejacobian was already set to reach here */
    781:     PetscCall(SNESSetJacobian(snes, J, B, NULL, NULL));
    782:     PetscCall(MatDestroy(&J));
    783:     PetscCall(MatDestroy(&B));
    784:   } else if (!snes->jacobian_pre) {
    785:     PetscDS   prob;
    786:     Mat       J, B;
    787:     PetscBool hasPrec = PETSC_FALSE;

    789:     J = snes->jacobian;
    790:     PetscCall(DMGetDS(dm, &prob));
    791:     if (prob) PetscCall(PetscDSHasJacobianPreconditioner(prob, &hasPrec));
    792:     if (J) PetscCall(PetscObjectReference((PetscObject)J));
    793:     else if (hasPrec) PetscCall(DMCreateMatrix(snes->dm, &J));
    794:     PetscCall(DMCreateMatrix(snes->dm, &B));
    795:     PetscCall(SNESSetJacobian(snes, J ? J : B, B, NULL, NULL));
    796:     PetscCall(MatDestroy(&J));
    797:     PetscCall(MatDestroy(&B));
    798:   }
    799:   {
    800:     KSP ksp;
    801:     PetscCall(SNESGetKSP(snes, &ksp));
    802:     PetscCall(KSPSetComputeOperators(ksp, KSPComputeOperators_SNES, snes));
    803:     PetscCall(DMCoarsenHookAdd(snes->dm, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, snes));
    804:   }
    805:   PetscFunctionReturn(PETSC_SUCCESS);
    806: }

    808: PETSC_EXTERN PetscErrorCode PetscMonitorPauseFinal_Internal(PetscInt, void *);

    810: static PetscErrorCode SNESMonitorPauseFinal_Internal(SNES snes)
    811: {
    812:   PetscFunctionBegin;
    813:   if (!snes->pauseFinal) PetscFunctionReturn(PETSC_SUCCESS);
    814:   PetscCall(PetscMonitorPauseFinal_Internal(snes->numbermonitors, snes->monitorcontext));
    815:   PetscFunctionReturn(PETSC_SUCCESS);
    816: }

    818: /*@C
    819:   SNESMonitorSetFromOptions - Sets a monitor function and viewer appropriate for the type indicated by the user

    821:   Collective

    823:   Input Parameters:
    824: + snes         - `SNES` object you wish to monitor
    825: . name         - the monitor type one is seeking
    826: . help         - message indicating what monitoring is done
    827: . manual       - manual page for the monitor
    828: . monitor      - the monitor function, this must use a `PetscViewerFormat` as its context
    829: - monitorsetup - a function that is called once ONLY if the user selected this monitor that may set additional features of the `SNES` or `PetscViewer` objects

    831:   Calling sequence of `monitor`:
    832: + snes - the nonlinear solver context
    833: . it   - the current iteration
    834: . r    - the current function norm
    835: - vf   - a `PetscViewerAndFormat` struct that contains the `PetscViewer` and `PetscViewerFormat` to use

    837:   Calling sequence of `monitorsetup`:
    838: + snes - the nonlinear solver context
    839: - vf   - a `PetscViewerAndFormat` struct that contains the `PetscViewer` and `PetscViewerFormat` to use

    841:   Options Database Key:
    842: . -name - trigger the use of this monitor in `SNESSetFromOptions()`

    844:   Level: advanced

    846: .seealso: [](ch_snes), `PetscOptionsCreateViewer()`, `PetscOptionsGetReal()`, `PetscOptionsHasName()`, `PetscOptionsGetString()`,
    847:           `PetscOptionsGetIntArray()`, `PetscOptionsGetRealArray()`, `PetscOptionsBool()`
    848:           `PetscOptionsInt()`, `PetscOptionsString()`, `PetscOptionsReal()`,
    849:           `PetscOptionsName()`, `PetscOptionsBegin()`, `PetscOptionsEnd()`, `PetscOptionsHeadBegin()`,
    850:           `PetscOptionsStringArray()`, `PetscOptionsRealArray()`, `PetscOptionsScalar()`,
    851:           `PetscOptionsBoolGroupBegin()`, `PetscOptionsBoolGroup()`, `PetscOptionsBoolGroupEnd()`,
    852:           `PetscOptionsFList()`, `PetscOptionsEList()`
    853: @*/
    854: PetscErrorCode SNESMonitorSetFromOptions(SNES snes, const char name[], const char help[], const char manual[], PetscErrorCode (*monitor)(SNES snes, PetscInt it, PetscReal r, PetscViewerAndFormat *vf), PetscErrorCode (*monitorsetup)(SNES snes, PetscViewerAndFormat *vf))
    855: {
    856:   PetscViewer       viewer;
    857:   PetscViewerFormat format;
    858:   PetscBool         flg;

    860:   PetscFunctionBegin;
    861:   PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, name, &viewer, &format, &flg));
    862:   if (flg) {
    863:     PetscViewerAndFormat *vf;
    864:     PetscCall(PetscViewerAndFormatCreate(viewer, format, &vf));
    865:     PetscCall(PetscViewerDestroy(&viewer));
    866:     if (monitorsetup) PetscCall((*monitorsetup)(snes, vf));
    867:     PetscCall(SNESMonitorSet(snes, (PetscErrorCode (*)(SNES, PetscInt, PetscReal, void *))monitor, vf, (PetscCtxDestroyFn *)PetscViewerAndFormatDestroy));
    868:   }
    869:   PetscFunctionReturn(PETSC_SUCCESS);
    870: }

    872: PetscErrorCode SNESEWSetFromOptions_Private(SNESKSPEW *kctx, PetscBool print_api, MPI_Comm comm, const char *prefix)
    873: {
    874:   const char *api = print_api ? "SNESKSPSetParametersEW" : NULL;

    876:   PetscFunctionBegin;
    877:   PetscOptionsBegin(comm, prefix, "Eisenstat and Walker type forcing options", "KSP");
    878:   PetscCall(PetscOptionsInt("-ksp_ew_version", "Version 1, 2 or 3", api, kctx->version, &kctx->version, NULL));
    879:   PetscCall(PetscOptionsReal("-ksp_ew_rtol0", "0 <= rtol0 < 1", api, kctx->rtol_0, &kctx->rtol_0, NULL));
    880:   kctx->rtol_max = PetscMax(kctx->rtol_0, kctx->rtol_max);
    881:   PetscCall(PetscOptionsReal("-ksp_ew_rtolmax", "0 <= rtolmax < 1", api, kctx->rtol_max, &kctx->rtol_max, NULL));
    882:   PetscCall(PetscOptionsReal("-ksp_ew_gamma", "0 <= gamma <= 1", api, kctx->gamma, &kctx->gamma, NULL));
    883:   PetscCall(PetscOptionsReal("-ksp_ew_alpha", "1 < alpha <= 2", api, kctx->alpha, &kctx->alpha, NULL));
    884:   PetscCall(PetscOptionsReal("-ksp_ew_alpha2", "alpha2", NULL, kctx->alpha2, &kctx->alpha2, NULL));
    885:   PetscCall(PetscOptionsReal("-ksp_ew_threshold", "0 < threshold < 1", api, kctx->threshold, &kctx->threshold, NULL));
    886:   PetscCall(PetscOptionsReal("-ksp_ew_v4_p1", "p1", NULL, kctx->v4_p1, &kctx->v4_p1, NULL));
    887:   PetscCall(PetscOptionsReal("-ksp_ew_v4_p2", "p2", NULL, kctx->v4_p2, &kctx->v4_p2, NULL));
    888:   PetscCall(PetscOptionsReal("-ksp_ew_v4_p3", "p3", NULL, kctx->v4_p3, &kctx->v4_p3, NULL));
    889:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m1", "Scaling when rk-1 in [p2,p3)", NULL, kctx->v4_m1, &kctx->v4_m1, NULL));
    890:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m2", "Scaling when rk-1 in [p3,+infty)", NULL, kctx->v4_m2, &kctx->v4_m2, NULL));
    891:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m3", "Threshold for successive rtol (0.1 in Eq.7)", NULL, kctx->v4_m3, &kctx->v4_m3, NULL));
    892:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m4", "Adaptation scaling (0.5 in Eq.7)", NULL, kctx->v4_m4, &kctx->v4_m4, NULL));
    893:   PetscOptionsEnd();
    894:   PetscFunctionReturn(PETSC_SUCCESS);
    895: }

    897: /*@
    898:   SNESSetFromOptions - Sets various `SNES` and `KSP` parameters from user options.

    900:   Collective

    902:   Input Parameter:
    903: . snes - the `SNES` context

    905:   Options Database Keys:
    906: + -snes_type <type>                                                            - newtonls, newtontr, ngmres, ncg, nrichardson, qn, vi, fas, `SNESType` for complete list
    907: . -snes_rtol <rtol>                                                            - relative decrease in tolerance norm from initial
    908: . -snes_atol <abstol>                                                          - absolute tolerance of residual norm
    909: . -snes_stol <stol>                                                            - convergence tolerance in terms of the norm of the change in the solution between steps
    910: . -snes_divergence_tolerance <divtol>                                          - if the residual goes above divtol*rnorm0, exit with divergence
    911: . -snes_max_it <max_it>                                                        - maximum number of iterations
    912: . -snes_max_funcs <max_funcs>                                                  - maximum number of function evaluations
    913: . -snes_force_iteration <force>                                                - force `SNESSolve()` to take at least one iteration
    914: . -snes_max_fail <max_fail>                                                    - maximum number of line search failures allowed before stopping, default is none
    915: . -snes_max_linear_solve_fail                                                  - number of linear solver failures before SNESSolve() stops
    916: . -snes_lag_preconditioner <lag>                                               - how often preconditioner is rebuilt (use -1 to never rebuild)
    917: . -snes_lag_preconditioner_persists <true,false>                               - retains the -snes_lag_preconditioner information across multiple SNESSolve()
    918: . -snes_lag_jacobian <lag>                                                     - how often Jacobian is rebuilt (use -1 to never rebuild)
    919: . -snes_lag_jacobian_persists <true,false>                                     - retains the -snes_lag_jacobian information across multiple SNESSolve()
    920: . -snes_convergence_test <default,skip,correct_pressure>                       - convergence test in nonlinear solver. default `SNESConvergedDefault()`. skip `SNESConvergedSkip()` means continue iterating until max_it or some other criterion is reached, saving expense of convergence test. correct_pressure `SNESConvergedCorrectPressure()` has special handling of a pressure null space.
    921: . -snes_monitor [ascii][:filename][:viewer format]                             - prints residual norm at each iteration. if no filename given prints to stdout
    922: . -snes_monitor_solution [ascii binary draw][:filename][:viewer format]        - plots solution at each iteration
    923: . -snes_monitor_residual [ascii binary draw][:filename][:viewer format]        - plots residual (not its norm) at each iteration
    924: . -snes_monitor_solution_update [ascii binary draw][:filename][:viewer format] - plots update to solution at each iteration
    925: . -snes_monitor_lg_residualnorm                                                - plots residual norm at each iteration
    926: . -snes_monitor_lg_range                                                       - plots residual norm at each iteration
    927: . -snes_monitor_pause_final                                                    - Pauses all monitor drawing after the solver ends
    928: . -snes_fd                                                                     - use finite differences to compute Jacobian; very slow, only for testing
    929: . -snes_fd_color                                                               - use finite differences with coloring to compute Jacobian
    930: . -snes_mf_ksp_monitor                                                         - if using matrix-free multiply then print h at each `KSP` iteration
    931: . -snes_converged_reason                                                       - print the reason for convergence/divergence after each solve
    932: . -npc_snes_type <type>                                                        - the `SNES` type to use as a nonlinear preconditioner
    933: . -snes_test_jacobian <optional threshold>                                     - compare the user provided Jacobian with one computed via finite differences to check for errors.  If a threshold is given, display only those entries whose difference is greater than the threshold.
    934: - -snes_test_jacobian_view                                                     - display the user provided Jacobian, the finite difference Jacobian and the difference between them to help users detect the location of errors in the user provided Jacobian.

    936:   Options Database Keys for Eisenstat-Walker method:
    937: + -snes_ksp_ew                       - use Eisenstat-Walker method for determining linear system convergence
    938: . -snes_ksp_ew_version ver           - version of  Eisenstat-Walker method
    939: . -snes_ksp_ew_rtol0 <rtol0>         - Sets rtol0
    940: . -snes_ksp_ew_rtolmax <rtolmax>     - Sets rtolmax
    941: . -snes_ksp_ew_gamma <gamma>         - Sets gamma
    942: . -snes_ksp_ew_alpha <alpha>         - Sets alpha
    943: . -snes_ksp_ew_alpha2 <alpha2>       - Sets alpha2
    944: - -snes_ksp_ew_threshold <threshold> - Sets threshold

    946:   Level: beginner

    948:   Notes:
    949:   To see all options, run your program with the -help option or consult the users manual

    951:   `SNES` supports three approaches for computing (approximate) Jacobians: user provided via `SNESSetJacobian()`, matrix-free using `MatCreateSNESMF()`,
    952:   and computing explicitly with
    953:   finite differences and coloring using `MatFDColoring`. It is also possible to use automatic differentiation and the `MatFDColoring` object.

    955: .seealso: [](ch_snes), `SNESType`, `SNESSetOptionsPrefix()`, `SNESResetFromOptions()`, `SNES`, `SNESCreate()`, `MatCreateSNESMF()`, `MatFDColoring`
    956: @*/
    957: PetscErrorCode SNESSetFromOptions(SNES snes)
    958: {
    959:   PetscBool   flg, pcset, persist, set;
    960:   PetscInt    i, indx, lag, grids, max_its, max_funcs;
    961:   const char *deft        = SNESNEWTONLS;
    962:   const char *convtests[] = {"default", "skip", "correct_pressure"};
    963:   SNESKSPEW  *kctx        = NULL;
    964:   char        type[256], monfilename[PETSC_MAX_PATH_LEN], ewprefix[256];
    965:   PCSide      pcside;
    966:   const char *optionsprefix;
    967:   PetscReal   rtol, abstol, stol;

    969:   PetscFunctionBegin;
    971:   PetscCall(SNESRegisterAll());
    972:   PetscObjectOptionsBegin((PetscObject)snes);
    973:   if (((PetscObject)snes)->type_name) deft = ((PetscObject)snes)->type_name;
    974:   PetscCall(PetscOptionsFList("-snes_type", "Nonlinear solver method", "SNESSetType", SNESList, deft, type, 256, &flg));
    975:   if (flg) {
    976:     PetscCall(SNESSetType(snes, type));
    977:   } else if (!((PetscObject)snes)->type_name) {
    978:     PetscCall(SNESSetType(snes, deft));
    979:   }

    981:   abstol    = snes->abstol;
    982:   rtol      = snes->rtol;
    983:   stol      = snes->stol;
    984:   max_its   = snes->max_its;
    985:   max_funcs = snes->max_funcs;
    986:   PetscCall(PetscOptionsReal("-snes_rtol", "Stop if decrease in function norm less than", "SNESSetTolerances", snes->rtol, &rtol, NULL));
    987:   PetscCall(PetscOptionsReal("-snes_atol", "Stop if function norm less than", "SNESSetTolerances", snes->abstol, &abstol, NULL));
    988:   PetscCall(PetscOptionsReal("-snes_stol", "Stop if step length less than", "SNESSetTolerances", snes->stol, &stol, NULL));
    989:   PetscCall(PetscOptionsInt("-snes_max_it", "Maximum iterations", "SNESSetTolerances", snes->max_its, &max_its, NULL));
    990:   PetscCall(PetscOptionsInt("-snes_max_funcs", "Maximum function evaluations", "SNESSetTolerances", snes->max_funcs, &max_funcs, NULL));
    991:   PetscCall(SNESSetTolerances(snes, abstol, rtol, stol, max_its, max_funcs));

    993:   PetscCall(PetscOptionsReal("-snes_divergence_tolerance", "Stop if residual norm increases by this factor", "SNESSetDivergenceTolerance", snes->divtol, &snes->divtol, &flg));
    994:   if (flg) PetscCall(SNESSetDivergenceTolerance(snes, snes->divtol));

    996:   PetscCall(PetscOptionsInt("-snes_max_fail", "Maximum nonlinear step failures", "SNESSetMaxNonlinearStepFailures", snes->maxFailures, &snes->maxFailures, &flg));
    997:   if (flg) PetscCall(SNESSetMaxNonlinearStepFailures(snes, snes->maxFailures));

    999:   PetscCall(PetscOptionsInt("-snes_max_linear_solve_fail", "Maximum failures in linear solves allowed", "SNESSetMaxLinearSolveFailures", snes->maxLinearSolveFailures, &snes->maxLinearSolveFailures, &flg));
    1000:   if (flg) PetscCall(SNESSetMaxLinearSolveFailures(snes, snes->maxLinearSolveFailures));

    1002:   PetscCall(PetscOptionsBool("-snes_error_if_not_converged", "Generate error if solver does not converge", "SNESSetErrorIfNotConverged", snes->errorifnotconverged, &snes->errorifnotconverged, NULL));
    1003:   PetscCall(PetscOptionsBool("-snes_force_iteration", "Force SNESSolve() to take at least one iteration", "SNESSetForceIteration", snes->forceiteration, &snes->forceiteration, NULL));
    1004:   PetscCall(PetscOptionsBool("-snes_check_jacobian_domain_error", "Check Jacobian domain error after Jacobian evaluation", "SNESCheckJacobianDomainError", snes->checkjacdomainerror, &snes->checkjacdomainerror, NULL));

    1006:   PetscCall(PetscOptionsInt("-snes_lag_preconditioner", "How often to rebuild preconditioner", "SNESSetLagPreconditioner", snes->lagpreconditioner, &lag, &flg));
    1007:   if (flg) {
    1008:     PetscCheck(lag != -1, PetscObjectComm((PetscObject)snes), PETSC_ERR_USER, "Cannot set the lag to -1 from the command line since the preconditioner must be built as least once, perhaps you mean -2");
    1009:     PetscCall(SNESSetLagPreconditioner(snes, lag));
    1010:   }
    1011:   PetscCall(PetscOptionsBool("-snes_lag_preconditioner_persists", "Preconditioner lagging through multiple SNES solves", "SNESSetLagPreconditionerPersists", snes->lagjac_persist, &persist, &flg));
    1012:   if (flg) PetscCall(SNESSetLagPreconditionerPersists(snes, persist));
    1013:   PetscCall(PetscOptionsInt("-snes_lag_jacobian", "How often to rebuild Jacobian", "SNESSetLagJacobian", snes->lagjacobian, &lag, &flg));
    1014:   if (flg) {
    1015:     PetscCheck(lag != -1, PetscObjectComm((PetscObject)snes), PETSC_ERR_USER, "Cannot set the lag to -1 from the command line since the Jacobian must be built as least once, perhaps you mean -2");
    1016:     PetscCall(SNESSetLagJacobian(snes, lag));
    1017:   }
    1018:   PetscCall(PetscOptionsBool("-snes_lag_jacobian_persists", "Jacobian lagging through multiple SNES solves", "SNESSetLagJacobianPersists", snes->lagjac_persist, &persist, &flg));
    1019:   if (flg) PetscCall(SNESSetLagJacobianPersists(snes, persist));

    1021:   PetscCall(PetscOptionsInt("-snes_grid_sequence", "Use grid sequencing to generate initial guess", "SNESSetGridSequence", snes->gridsequence, &grids, &flg));
    1022:   if (flg) PetscCall(SNESSetGridSequence(snes, grids));

    1024:   PetscCall(PetscOptionsEList("-snes_convergence_test", "Convergence test", "SNESSetConvergenceTest", convtests, PETSC_STATIC_ARRAY_LENGTH(convtests), "default", &indx, &flg));
    1025:   if (flg) {
    1026:     switch (indx) {
    1027:     case 0:
    1028:       PetscCall(SNESSetConvergenceTest(snes, SNESConvergedDefault, NULL, NULL));
    1029:       break;
    1030:     case 1:
    1031:       PetscCall(SNESSetConvergenceTest(snes, SNESConvergedSkip, NULL, NULL));
    1032:       break;
    1033:     case 2:
    1034:       PetscCall(SNESSetConvergenceTest(snes, SNESConvergedCorrectPressure, NULL, NULL));
    1035:       break;
    1036:     }
    1037:   }

    1039:   PetscCall(PetscOptionsEList("-snes_norm_schedule", "SNES Norm schedule", "SNESSetNormSchedule", SNESNormSchedules, 5, "function", &indx, &flg));
    1040:   if (flg) PetscCall(SNESSetNormSchedule(snes, (SNESNormSchedule)indx));

    1042:   PetscCall(PetscOptionsEList("-snes_function_type", "SNES Norm schedule", "SNESSetFunctionType", SNESFunctionTypes, 2, "unpreconditioned", &indx, &flg));
    1043:   if (flg) PetscCall(SNESSetFunctionType(snes, (SNESFunctionType)indx));

    1045:   kctx = (SNESKSPEW *)snes->kspconvctx;

    1047:   PetscCall(PetscOptionsBool("-snes_ksp_ew", "Use Eisentat-Walker linear system convergence test", "SNESKSPSetUseEW", snes->ksp_ewconv, &snes->ksp_ewconv, NULL));

    1049:   PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    1050:   PetscCall(PetscSNPrintf(ewprefix, sizeof(ewprefix), "%s%s", optionsprefix ? optionsprefix : "", "snes_"));
    1051:   PetscCall(SNESEWSetFromOptions_Private(kctx, PETSC_TRUE, PetscObjectComm((PetscObject)snes), ewprefix));

    1053:   flg = PETSC_FALSE;
    1054:   PetscCall(PetscOptionsBool("-snes_monitor_cancel", "Remove all monitors", "SNESMonitorCancel", flg, &flg, &set));
    1055:   if (set && flg) PetscCall(SNESMonitorCancel(snes));

    1057:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor", "Monitor norm of function", "SNESMonitorDefault", SNESMonitorDefault, SNESMonitorDefaultSetUp));
    1058:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_short", "Monitor norm of function with fewer digits", "SNESMonitorDefaultShort", SNESMonitorDefaultShort, NULL));
    1059:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_range", "Monitor range of elements of function", "SNESMonitorRange", SNESMonitorRange, NULL));

    1061:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_ratio", "Monitor ratios of the norm of function for consecutive steps", "SNESMonitorRatio", SNESMonitorRatio, SNESMonitorRatioSetUp));
    1062:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_field", "Monitor norm of function (split into fields)", "SNESMonitorDefaultField", SNESMonitorDefaultField, NULL));
    1063:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_solution", "View solution at each iteration", "SNESMonitorSolution", SNESMonitorSolution, NULL));
    1064:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_solution_update", "View correction at each iteration", "SNESMonitorSolutionUpdate", SNESMonitorSolutionUpdate, NULL));
    1065:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_residual", "View residual at each iteration", "SNESMonitorResidual", SNESMonitorResidual, NULL));
    1066:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_jacupdate_spectrum", "Print the change in the spectrum of the Jacobian", "SNESMonitorJacUpdateSpectrum", SNESMonitorJacUpdateSpectrum, NULL));
    1067:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_fields", "Monitor norm of function per field", "SNESMonitorSet", SNESMonitorFields, NULL));
    1068:   PetscCall(PetscOptionsBool("-snes_monitor_pause_final", "Pauses all draw monitors at the final iterate", "SNESMonitorPauseFinal_Internal", PETSC_FALSE, &snes->pauseFinal, NULL));

    1070:   PetscCall(PetscOptionsString("-snes_monitor_python", "Use Python function", "SNESMonitorSet", NULL, monfilename, sizeof(monfilename), &flg));
    1071:   if (flg) PetscCall(PetscPythonMonitorSet((PetscObject)snes, monfilename));

    1073:   flg = PETSC_FALSE;
    1074:   PetscCall(PetscOptionsBool("-snes_monitor_lg_range", "Plot function range at each iteration", "SNESMonitorLGRange", flg, &flg, NULL));
    1075:   if (flg) {
    1076:     PetscViewer ctx;

    1078:     PetscCall(PetscViewerDrawOpen(PetscObjectComm((PetscObject)snes), NULL, NULL, PETSC_DECIDE, PETSC_DECIDE, 400, 300, &ctx));
    1079:     PetscCall(SNESMonitorSet(snes, SNESMonitorLGRange, ctx, (PetscCtxDestroyFn *)PetscViewerDestroy));
    1080:   }

    1082:   PetscCall(PetscViewerDestroy(&snes->convergedreasonviewer));
    1083:   PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_converged_reason", &snes->convergedreasonviewer, &snes->convergedreasonformat, NULL));
    1084:   flg = PETSC_FALSE;
    1085:   PetscCall(PetscOptionsBool("-snes_converged_reason_view_cancel", "Remove all converged reason viewers", "SNESConvergedReasonViewCancel", flg, &flg, &set));
    1086:   if (set && flg) PetscCall(SNESConvergedReasonViewCancel(snes));

    1088:   flg = PETSC_FALSE;
    1089:   PetscCall(PetscOptionsBool("-snes_fd", "Use finite differences (slow) to compute Jacobian", "SNESComputeJacobianDefault", flg, &flg, NULL));
    1090:   if (flg) {
    1091:     void *functx;
    1092:     DM    dm;
    1093:     PetscCall(SNESGetDM(snes, &dm));
    1094:     PetscCall(DMSNESUnsetJacobianContext_Internal(dm));
    1095:     PetscCall(SNESGetFunction(snes, NULL, NULL, &functx));
    1096:     PetscCall(SNESSetJacobian(snes, snes->jacobian, snes->jacobian_pre, SNESComputeJacobianDefault, functx));
    1097:     PetscCall(PetscInfo(snes, "Setting default finite difference Jacobian matrix\n"));
    1098:   }

    1100:   flg = PETSC_FALSE;
    1101:   PetscCall(PetscOptionsBool("-snes_fd_function", "Use finite differences (slow) to compute function from user objective", "SNESObjectiveComputeFunctionDefaultFD", flg, &flg, NULL));
    1102:   if (flg) PetscCall(SNESSetFunction(snes, NULL, SNESObjectiveComputeFunctionDefaultFD, NULL));

    1104:   flg = PETSC_FALSE;
    1105:   PetscCall(PetscOptionsBool("-snes_fd_color", "Use finite differences with coloring to compute Jacobian", "SNESComputeJacobianDefaultColor", flg, &flg, NULL));
    1106:   if (flg) {
    1107:     DM dm;
    1108:     PetscCall(SNESGetDM(snes, &dm));
    1109:     PetscCall(DMSNESUnsetJacobianContext_Internal(dm));
    1110:     PetscCall(SNESSetJacobian(snes, snes->jacobian, snes->jacobian_pre, SNESComputeJacobianDefaultColor, NULL));
    1111:     PetscCall(PetscInfo(snes, "Setting default finite difference coloring Jacobian matrix\n"));
    1112:   }

    1114:   flg = PETSC_FALSE;
    1115:   PetscCall(PetscOptionsBool("-snes_mf_operator", "Use a Matrix-Free Jacobian with user-provided preconditioner matrix", "SNESSetUseMatrixFree", PETSC_FALSE, &snes->mf_operator, &flg));
    1116:   if (flg && snes->mf_operator) {
    1117:     snes->mf_operator = PETSC_TRUE;
    1118:     snes->mf          = PETSC_TRUE;
    1119:   }
    1120:   flg = PETSC_FALSE;
    1121:   PetscCall(PetscOptionsBool("-snes_mf", "Use a Matrix-Free Jacobian with no preconditioner matrix", "SNESSetUseMatrixFree", PETSC_FALSE, &snes->mf, &flg));
    1122:   if (!flg && snes->mf_operator) snes->mf = PETSC_TRUE;
    1123:   PetscCall(PetscOptionsInt("-snes_mf_version", "Matrix-Free routines version 1 or 2", "None", snes->mf_version, &snes->mf_version, NULL));

    1125:   flg = PETSC_FALSE;
    1126:   PetscCall(SNESGetNPCSide(snes, &pcside));
    1127:   PetscCall(PetscOptionsEnum("-snes_npc_side", "SNES nonlinear preconditioner side", "SNESSetNPCSide", PCSides, (PetscEnum)pcside, (PetscEnum *)&pcside, &flg));
    1128:   if (flg) PetscCall(SNESSetNPCSide(snes, pcside));

    1130: #if defined(PETSC_HAVE_SAWS)
    1131:   /*
    1132:     Publish convergence information using SAWs
    1133:   */
    1134:   flg = PETSC_FALSE;
    1135:   PetscCall(PetscOptionsBool("-snes_monitor_saws", "Publish SNES progress using SAWs", "SNESMonitorSet", flg, &flg, NULL));
    1136:   if (flg) {
    1137:     void *ctx;
    1138:     PetscCall(SNESMonitorSAWsCreate(snes, &ctx));
    1139:     PetscCall(SNESMonitorSet(snes, SNESMonitorSAWs, ctx, SNESMonitorSAWsDestroy));
    1140:   }
    1141: #endif
    1142: #if defined(PETSC_HAVE_SAWS)
    1143:   {
    1144:     PetscBool set;
    1145:     flg = PETSC_FALSE;
    1146:     PetscCall(PetscOptionsBool("-snes_saws_block", "Block for SAWs at end of SNESSolve", "PetscObjectSAWsBlock", ((PetscObject)snes)->amspublishblock, &flg, &set));
    1147:     if (set) PetscCall(PetscObjectSAWsSetBlock((PetscObject)snes, flg));
    1148:   }
    1149: #endif

    1151:   for (i = 0; i < numberofsetfromoptions; i++) PetscCall((*othersetfromoptions[i])(snes));

    1153:   PetscTryTypeMethod(snes, setfromoptions, PetscOptionsObject);

    1155:   /* process any options handlers added with PetscObjectAddOptionsHandler() */
    1156:   PetscCall(PetscObjectProcessOptionsHandlers((PetscObject)snes, PetscOptionsObject));
    1157:   PetscOptionsEnd();

    1159:   if (snes->linesearch) {
    1160:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    1161:     PetscCall(SNESLineSearchSetFromOptions(snes->linesearch));
    1162:   }

    1164:   if (snes->usesksp) {
    1165:     if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));
    1166:     PetscCall(KSPSetOperators(snes->ksp, snes->jacobian, snes->jacobian_pre));
    1167:     PetscCall(KSPSetFromOptions(snes->ksp));
    1168:   }

    1170:   /* if user has set the SNES NPC type via options database, create it. */
    1171:   PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    1172:   PetscCall(PetscOptionsHasName(((PetscObject)snes)->options, optionsprefix, "-npc_snes_type", &pcset));
    1173:   if (pcset && (!snes->npc)) PetscCall(SNESGetNPC(snes, &snes->npc));
    1174:   if (snes->npc) PetscCall(SNESSetFromOptions(snes->npc));
    1175:   snes->setfromoptionscalled++;
    1176:   PetscFunctionReturn(PETSC_SUCCESS);
    1177: }

    1179: /*@
    1180:   SNESResetFromOptions - Sets various `SNES` and `KSP` parameters from user options ONLY if the `SNESSetFromOptions()` was previously called

    1182:   Collective

    1184:   Input Parameter:
    1185: . snes - the `SNES` context

    1187:   Level: advanced

    1189: .seealso: [](ch_snes), `SNES`, `SNESSetFromOptions()`, `SNESSetOptionsPrefix()`
    1190: @*/
    1191: PetscErrorCode SNESResetFromOptions(SNES snes)
    1192: {
    1193:   PetscFunctionBegin;
    1194:   if (snes->setfromoptionscalled) PetscCall(SNESSetFromOptions(snes));
    1195:   PetscFunctionReturn(PETSC_SUCCESS);
    1196: }

    1198: /*@C
    1199:   SNESSetComputeApplicationContext - Sets an optional function to compute a user-defined context for
    1200:   the nonlinear solvers.

    1202:   Logically Collective; No Fortran Support

    1204:   Input Parameters:
    1205: + snes    - the `SNES` context
    1206: . compute - function to compute the context
    1207: - destroy - function to destroy the context, see `PetscCtxDestroyFn` for the calling sequence

    1209:   Calling sequence of `compute`:
    1210: + snes - the `SNES` context
    1211: - ctx  - context to be computed

    1213:   Level: intermediate

    1215:   Note:
    1216:   This routine is useful if you are performing grid sequencing or using `SNESFAS` and need the appropriate context generated for each level.

    1218:   Use `SNESSetApplicationContext()` to see the context immediately

    1220: .seealso: [](ch_snes), `SNESGetApplicationContext()`, `SNESSetApplicationContext()`, `PetscCtxDestroyFn`
    1221: @*/
    1222: PetscErrorCode SNESSetComputeApplicationContext(SNES snes, PetscErrorCode (*compute)(SNES snes, void **ctx), PetscCtxDestroyFn *destroy)
    1223: {
    1224:   PetscFunctionBegin;
    1226:   snes->ops->usercompute = compute;
    1227:   snes->ops->ctxdestroy  = destroy;
    1228:   PetscFunctionReturn(PETSC_SUCCESS);
    1229: }

    1231: /*@
    1232:   SNESSetApplicationContext - Sets the optional user-defined context for the nonlinear solvers.

    1234:   Logically Collective

    1236:   Input Parameters:
    1237: + snes - the `SNES` context
    1238: - ctx  - the user context

    1240:   Level: intermediate

    1242:   Notes:
    1243:   Users can provide a context when constructing the `SNES` options and then access it inside their function, Jacobian computation, or other evaluation function
    1244:   with `SNESGetApplicationContext()`

    1246:   To provide a function that computes the context for you use `SNESSetComputeApplicationContext()`

    1248:   Fortran Note:
    1249:   This only works when `ctx` is a Fortran derived type (it cannot be a `PetscObject`), we recommend writing a Fortran interface definition for this
    1250:   function that tells the Fortran compiler the derived data type that is passed in as the `ctx` argument. See `SNESGetApplicationContext()` for
    1251:   an example.

    1253: .seealso: [](ch_snes), `SNES`, `SNESSetComputeApplicationContext()`, `SNESGetApplicationContext()`
    1254: @*/
    1255: PetscErrorCode SNESSetApplicationContext(SNES snes, void *ctx)
    1256: {
    1257:   KSP ksp;

    1259:   PetscFunctionBegin;
    1261:   PetscCall(SNESGetKSP(snes, &ksp));
    1262:   PetscCall(KSPSetApplicationContext(ksp, ctx));
    1263:   snes->ctx = ctx;
    1264:   PetscFunctionReturn(PETSC_SUCCESS);
    1265: }

    1267: /*@
    1268:   SNESGetApplicationContext - Gets the user-defined context for the
    1269:   nonlinear solvers set with `SNESGetApplicationContext()` or `SNESSetComputeApplicationContext()`

    1271:   Not Collective

    1273:   Input Parameter:
    1274: . snes - `SNES` context

    1276:   Output Parameter:
    1277: . ctx - user context

    1279:   Level: intermediate

    1281:   Fortran Notes:
    1282:   This only works when the context is a Fortran derived type (it cannot be a `PetscObject`) and you **must** write a Fortran interface definition for this
    1283:   function that tells the Fortran compiler the derived data type that is returned as the `ctx` argument. For example,
    1284: .vb
    1285:   Interface SNESGetApplicationContext
    1286:     Subroutine SNESGetApplicationContext(snes,ctx,ierr)
    1287:   #include <petsc/finclude/petscsnes.h>
    1288:       use petscsnes
    1289:       SNES snes
    1290:       type(tUsertype), pointer :: ctx
    1291:       PetscErrorCode ierr
    1292:     End Subroutine
    1293:   End Interface SNESGetApplicationContext
    1294: .ve

    1296:   The prototpye for `ctx` must be
    1297: .vb
    1298:   type(tUsertype), pointer :: ctx
    1299: .ve

    1301: .seealso: [](ch_snes), `SNESSetApplicationContext()`, `SNESSetComputeApplicationContext()`
    1302: @*/
    1303: PetscErrorCode SNESGetApplicationContext(SNES snes, PeCtx ctx)
    1304: {
    1305:   PetscFunctionBegin;
    1307:   *(void **)ctx = snes->ctx;
    1308:   PetscFunctionReturn(PETSC_SUCCESS);
    1309: }

    1311: /*@
    1312:   SNESSetUseMatrixFree - indicates that `SNES` should use matrix-free finite difference matrix-vector products to apply the Jacobian.

    1314:   Logically Collective

    1316:   Input Parameters:
    1317: + snes        - `SNES` context
    1318: . mf_operator - use matrix-free only for the Amat used by `SNESSetJacobian()`, this means the user provided Pmat will continue to be used
    1319: - mf          - use matrix-free for both the Amat and Pmat used by `SNESSetJacobian()`, both the Amat and Pmat set in `SNESSetJacobian()` will be ignored. With
    1320:                 this option no matrix-element based preconditioners can be used in the linear solve since the matrix won't be explicitly available

    1322:   Options Database Keys:
    1323: + -snes_mf_operator - use matrix-free only for the mat operator
    1324: . -snes_mf          - use matrix-free for both the mat and pmat operator
    1325: . -snes_fd_color    - compute the Jacobian via coloring and finite differences.
    1326: - -snes_fd          - compute the Jacobian via finite differences (slow)

    1328:   Level: intermediate

    1330:   Note:
    1331:   `SNES` supports three approaches for computing (approximate) Jacobians: user provided via `SNESSetJacobian()`, matrix-free using `MatCreateSNESMF()`,
    1332:   and computing explicitly with
    1333:   finite differences and coloring using `MatFDColoring`. It is also possible to use automatic differentiation and the `MatFDColoring` object.

    1335: .seealso: [](ch_snes), `SNES`, `SNESGetUseMatrixFree()`, `MatCreateSNESMF()`, `SNESComputeJacobianDefaultColor()`, `MatFDColoring`
    1336: @*/
    1337: PetscErrorCode SNESSetUseMatrixFree(SNES snes, PetscBool mf_operator, PetscBool mf)
    1338: {
    1339:   PetscFunctionBegin;
    1343:   snes->mf          = mf_operator ? PETSC_TRUE : mf;
    1344:   snes->mf_operator = mf_operator;
    1345:   PetscFunctionReturn(PETSC_SUCCESS);
    1346: }

    1348: /*@
    1349:   SNESGetUseMatrixFree - indicates if the `SNES` uses matrix-free finite difference matrix vector products to apply the Jacobian.

    1351:   Not Collective, but the resulting flags will be the same on all MPI processes

    1353:   Input Parameter:
    1354: . snes - `SNES` context

    1356:   Output Parameters:
    1357: + mf_operator - use matrix-free only for the Amat used by `SNESSetJacobian()`, this means the user provided Pmat will continue to be used
    1358: - mf          - use matrix-free for both the Amat and Pmat used by `SNESSetJacobian()`, both the Amat and Pmat set in `SNESSetJacobian()` will be ignored

    1360:   Level: intermediate

    1362: .seealso: [](ch_snes), `SNES`, `SNESSetUseMatrixFree()`, `MatCreateSNESMF()`
    1363: @*/
    1364: PetscErrorCode SNESGetUseMatrixFree(SNES snes, PetscBool *mf_operator, PetscBool *mf)
    1365: {
    1366:   PetscFunctionBegin;
    1368:   if (mf) *mf = snes->mf;
    1369:   if (mf_operator) *mf_operator = snes->mf_operator;
    1370:   PetscFunctionReturn(PETSC_SUCCESS);
    1371: }

    1373: /*@
    1374:   SNESGetIterationNumber - Gets the number of nonlinear iterations completed in the current or most recent `SNESSolve()`

    1376:   Not Collective

    1378:   Input Parameter:
    1379: . snes - `SNES` context

    1381:   Output Parameter:
    1382: . iter - iteration number

    1384:   Level: intermediate

    1386:   Notes:
    1387:   For example, during the computation of iteration 2 this would return 1.

    1389:   This is useful for using lagged Jacobians (where one does not recompute the
    1390:   Jacobian at each `SNES` iteration). For example, the code
    1391: .vb
    1392:       ierr = SNESGetIterationNumber(snes,&it);
    1393:       if (!(it % 2)) {
    1394:         [compute Jacobian here]
    1395:       }
    1396: .ve
    1397:   can be used in your function that computes the Jacobian to cause the Jacobian to be
    1398:   recomputed every second `SNES` iteration. See also `SNESSetLagJacobian()`

    1400:   After the `SNES` solve is complete this will return the number of nonlinear iterations used.

    1402: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetLagJacobian()`, `SNESGetLinearSolveIterations()`, `SNESSetMonitor()`
    1403: @*/
    1404: PetscErrorCode SNESGetIterationNumber(SNES snes, PetscInt *iter)
    1405: {
    1406:   PetscFunctionBegin;
    1408:   PetscAssertPointer(iter, 2);
    1409:   *iter = snes->iter;
    1410:   PetscFunctionReturn(PETSC_SUCCESS);
    1411: }

    1413: /*@
    1414:   SNESSetIterationNumber - Sets the current iteration number.

    1416:   Not Collective

    1418:   Input Parameters:
    1419: + snes - `SNES` context
    1420: - iter - iteration number

    1422:   Level: developer

    1424:   Note:
    1425:   This should only be called inside a `SNES` nonlinear solver.

    1427: .seealso: [](ch_snes), `SNESGetLinearSolveIterations()`
    1428: @*/
    1429: PetscErrorCode SNESSetIterationNumber(SNES snes, PetscInt iter)
    1430: {
    1431:   PetscFunctionBegin;
    1433:   PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
    1434:   snes->iter = iter;
    1435:   PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
    1436:   PetscFunctionReturn(PETSC_SUCCESS);
    1437: }

    1439: /*@
    1440:   SNESGetNonlinearStepFailures - Gets the number of unsuccessful steps
    1441:   attempted by the nonlinear solver in the current or most recent `SNESSolve()` .

    1443:   Not Collective

    1445:   Input Parameter:
    1446: . snes - `SNES` context

    1448:   Output Parameter:
    1449: . nfails - number of unsuccessful steps attempted

    1451:   Level: intermediate

    1453:   Note:
    1454:   This counter is reset to zero for each successive call to `SNESSolve()`.

    1456: .seealso: [](ch_snes), `SNES`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`,
    1457:           `SNESSetMaxNonlinearStepFailures()`, `SNESGetMaxNonlinearStepFailures()`
    1458: @*/
    1459: PetscErrorCode SNESGetNonlinearStepFailures(SNES snes, PetscInt *nfails)
    1460: {
    1461:   PetscFunctionBegin;
    1463:   PetscAssertPointer(nfails, 2);
    1464:   *nfails = snes->numFailures;
    1465:   PetscFunctionReturn(PETSC_SUCCESS);
    1466: }

    1468: /*@
    1469:   SNESSetMaxNonlinearStepFailures - Sets the maximum number of unsuccessful steps
    1470:   attempted by the nonlinear solver before it gives up and returns unconverged or generates an error

    1472:   Not Collective

    1474:   Input Parameters:
    1475: + snes     - `SNES` context
    1476: - maxFails - maximum of unsuccessful steps allowed, use `PETSC_UNLIMITED` to have no limit on the number of failures

    1478:   Options Database Key:
    1479: . -snes_max_fail <n> - maximum number of unsuccessful steps allowed

    1481:   Level: intermediate

    1483:   Developer Note:
    1484:   The options database key is wrong for this function name

    1486: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`,
    1487:           `SNESGetMaxNonlinearStepFailures()`, `SNESGetNonlinearStepFailures()`
    1488: @*/
    1489: PetscErrorCode SNESSetMaxNonlinearStepFailures(SNES snes, PetscInt maxFails)
    1490: {
    1491:   PetscFunctionBegin;

    1494:   if (maxFails == PETSC_UNLIMITED) {
    1495:     snes->maxFailures = PETSC_INT_MAX;
    1496:   } else {
    1497:     PetscCheck(maxFails >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Cannot have a negative maximum number of failures");
    1498:     snes->maxFailures = maxFails;
    1499:   }
    1500:   PetscFunctionReturn(PETSC_SUCCESS);
    1501: }

    1503: /*@
    1504:   SNESGetMaxNonlinearStepFailures - Gets the maximum number of unsuccessful steps
    1505:   attempted by the nonlinear solver before it gives up and returns unconverged or generates an error

    1507:   Not Collective

    1509:   Input Parameter:
    1510: . snes - `SNES` context

    1512:   Output Parameter:
    1513: . maxFails - maximum of unsuccessful steps

    1515:   Level: intermediate

    1517: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`,
    1518:           `SNESSetMaxNonlinearStepFailures()`, `SNESGetNonlinearStepFailures()`
    1519: @*/
    1520: PetscErrorCode SNESGetMaxNonlinearStepFailures(SNES snes, PetscInt *maxFails)
    1521: {
    1522:   PetscFunctionBegin;
    1524:   PetscAssertPointer(maxFails, 2);
    1525:   *maxFails = snes->maxFailures;
    1526:   PetscFunctionReturn(PETSC_SUCCESS);
    1527: }

    1529: /*@
    1530:   SNESGetNumberFunctionEvals - Gets the number of user provided function evaluations
    1531:   done by the `SNES` object in the current or most recent `SNESSolve()`

    1533:   Not Collective

    1535:   Input Parameter:
    1536: . snes - `SNES` context

    1538:   Output Parameter:
    1539: . nfuncs - number of evaluations

    1541:   Level: intermediate

    1543:   Note:
    1544:   Reset every time `SNESSolve()` is called unless `SNESSetCountersReset()` is used.

    1546: .seealso: [](ch_snes), `SNES`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`, `SNESSetCountersReset()`
    1547: @*/
    1548: PetscErrorCode SNESGetNumberFunctionEvals(SNES snes, PetscInt *nfuncs)
    1549: {
    1550:   PetscFunctionBegin;
    1552:   PetscAssertPointer(nfuncs, 2);
    1553:   *nfuncs = snes->nfuncs;
    1554:   PetscFunctionReturn(PETSC_SUCCESS);
    1555: }

    1557: /*@
    1558:   SNESGetLinearSolveFailures - Gets the number of failed (non-converged)
    1559:   linear solvers in the current or most recent `SNESSolve()`

    1561:   Not Collective

    1563:   Input Parameter:
    1564: . snes - `SNES` context

    1566:   Output Parameter:
    1567: . nfails - number of failed solves

    1569:   Options Database Key:
    1570: . -snes_max_linear_solve_fail <num> - The number of failures before the solve is terminated

    1572:   Level: intermediate

    1574:   Note:
    1575:   This counter is reset to zero for each successive call to `SNESSolve()`.

    1577: .seealso: [](ch_snes), `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`
    1578: @*/
    1579: PetscErrorCode SNESGetLinearSolveFailures(SNES snes, PetscInt *nfails)
    1580: {
    1581:   PetscFunctionBegin;
    1583:   PetscAssertPointer(nfails, 2);
    1584:   *nfails = snes->numLinearSolveFailures;
    1585:   PetscFunctionReturn(PETSC_SUCCESS);
    1586: }

    1588: /*@
    1589:   SNESSetMaxLinearSolveFailures - the number of failed linear solve attempts
    1590:   allowed before `SNES` returns with a diverged reason of `SNES_DIVERGED_LINEAR_SOLVE`

    1592:   Logically Collective

    1594:   Input Parameters:
    1595: + snes     - `SNES` context
    1596: - maxFails - maximum allowed linear solve failures, use `PETSC_UNLIMITED` to have no limit on the number of failures

    1598:   Options Database Key:
    1599: . -snes_max_linear_solve_fail <num> - The number of failures before the solve is terminated

    1601:   Level: intermediate

    1603:   Note:
    1604:   By default this is 0; that is `SNES` returns on the first failed linear solve

    1606:   Developer Note:
    1607:   The options database key is wrong for this function name

    1609: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetLinearSolveFailures()`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`
    1610: @*/
    1611: PetscErrorCode SNESSetMaxLinearSolveFailures(SNES snes, PetscInt maxFails)
    1612: {
    1613:   PetscFunctionBegin;

    1617:   if (maxFails == PETSC_UNLIMITED) {
    1618:     snes->maxLinearSolveFailures = PETSC_INT_MAX;
    1619:   } else {
    1620:     PetscCheck(maxFails >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Cannot have a negative maximum number of failures");
    1621:     snes->maxLinearSolveFailures = maxFails;
    1622:   }
    1623:   PetscFunctionReturn(PETSC_SUCCESS);
    1624: }

    1626: /*@
    1627:   SNESGetMaxLinearSolveFailures - gets the maximum number of linear solve failures that
    1628:   are allowed before `SNES` returns as unsuccessful

    1630:   Not Collective

    1632:   Input Parameter:
    1633: . snes - `SNES` context

    1635:   Output Parameter:
    1636: . maxFails - maximum of unsuccessful solves allowed

    1638:   Level: intermediate

    1640:   Note:
    1641:   By default this is 1; that is `SNES` returns on the first failed linear solve

    1643: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`,
    1644: @*/
    1645: PetscErrorCode SNESGetMaxLinearSolveFailures(SNES snes, PetscInt *maxFails)
    1646: {
    1647:   PetscFunctionBegin;
    1649:   PetscAssertPointer(maxFails, 2);
    1650:   *maxFails = snes->maxLinearSolveFailures;
    1651:   PetscFunctionReturn(PETSC_SUCCESS);
    1652: }

    1654: /*@
    1655:   SNESGetLinearSolveIterations - Gets the total number of linear iterations
    1656:   used by the nonlinear solver in the most recent `SNESSolve()`

    1658:   Not Collective

    1660:   Input Parameter:
    1661: . snes - `SNES` context

    1663:   Output Parameter:
    1664: . lits - number of linear iterations

    1666:   Level: intermediate

    1668:   Notes:
    1669:   This counter is reset to zero for each successive call to `SNESSolve()` unless `SNESSetCountersReset()` is used.

    1671:   If the linear solver fails inside the `SNESSolve()` the iterations for that call to the linear solver are not included. If you wish to count them
    1672:   then call `KSPGetIterationNumber()` after the failed solve.

    1674: .seealso: [](ch_snes), `SNES`, `SNESGetIterationNumber()`, `SNESGetLinearSolveFailures()`, `SNESGetMaxLinearSolveFailures()`, `SNESSetCountersReset()`
    1675: @*/
    1676: PetscErrorCode SNESGetLinearSolveIterations(SNES snes, PetscInt *lits)
    1677: {
    1678:   PetscFunctionBegin;
    1680:   PetscAssertPointer(lits, 2);
    1681:   *lits = snes->linear_its;
    1682:   PetscFunctionReturn(PETSC_SUCCESS);
    1683: }

    1685: /*@
    1686:   SNESSetCountersReset - Sets whether or not the counters for linear iterations and function evaluations
    1687:   are reset every time `SNESSolve()` is called.

    1689:   Logically Collective

    1691:   Input Parameters:
    1692: + snes  - `SNES` context
    1693: - reset - whether to reset the counters or not, defaults to `PETSC_TRUE`

    1695:   Level: developer

    1697: .seealso: [](ch_snes), `SNESGetNumberFunctionEvals()`, `SNESGetLinearSolveIterations()`, `SNESGetNPC()`
    1698: @*/
    1699: PetscErrorCode SNESSetCountersReset(SNES snes, PetscBool reset)
    1700: {
    1701:   PetscFunctionBegin;
    1704:   snes->counters_reset = reset;
    1705:   PetscFunctionReturn(PETSC_SUCCESS);
    1706: }

    1708: /*@
    1709:   SNESResetCounters - Reset counters for linear iterations and function evaluations.

    1711:   Logically Collective

    1713:   Input Parameters:
    1714: . snes - `SNES` context

    1716:   Level: developer

    1718:   Note:
    1719:   It honors the flag set with `SNESSetCountersReset()`

    1721: .seealso: [](ch_snes), `SNESGetNumberFunctionEvals()`, `SNESGetLinearSolveIterations()`, `SNESGetNPC()`
    1722: @*/
    1723: PetscErrorCode SNESResetCounters(SNES snes)
    1724: {
    1725:   PetscFunctionBegin;
    1727:   if (snes->counters_reset) {
    1728:     snes->nfuncs      = 0;
    1729:     snes->linear_its  = 0;
    1730:     snes->numFailures = 0;
    1731:   }
    1732:   PetscFunctionReturn(PETSC_SUCCESS);
    1733: }

    1735: /*@
    1736:   SNESSetKSP - Sets a `KSP` context for the `SNES` object to use

    1738:   Not Collective, but the `SNES` and `KSP` objects must live on the same `MPI_Comm`

    1740:   Input Parameters:
    1741: + snes - the `SNES` context
    1742: - ksp  - the `KSP` context

    1744:   Level: developer

    1746:   Notes:
    1747:   The `SNES` object already has its `KSP` object, you can obtain with `SNESGetKSP()`
    1748:   so this routine is rarely needed.

    1750:   The `KSP` object that is already in the `SNES` object has its reference count
    1751:   decreased by one when this is called.

    1753: .seealso: [](ch_snes), `SNES`, `KSP`, `KSPGetPC()`, `SNESCreate()`, `KSPCreate()`
    1754: @*/
    1755: PetscErrorCode SNESSetKSP(SNES snes, KSP ksp)
    1756: {
    1757:   PetscFunctionBegin;
    1760:   PetscCheckSameComm(snes, 1, ksp, 2);
    1761:   PetscCall(PetscObjectReference((PetscObject)ksp));
    1762:   if (snes->ksp) PetscCall(PetscObjectDereference((PetscObject)snes->ksp));
    1763:   snes->ksp = ksp;
    1764:   PetscFunctionReturn(PETSC_SUCCESS);
    1765: }

    1767: /*@
    1768:   SNESParametersInitialize - Sets all the parameters in `snes` to their default value (when `SNESCreate()` was called) if they
    1769:   currently contain default values

    1771:   Collective

    1773:   Input Parameter:
    1774: . snes - the `SNES` object

    1776:   Level: developer

    1778:   Developer Note:
    1779:   This is called by all the `SNESCreate_XXX()` routines.

    1781: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESDestroy()`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobian()`,
    1782:           `PetscObjectParameterSetDefault()`
    1783: @*/
    1784: PetscErrorCode SNESParametersInitialize(SNES snes)
    1785: {
    1786:   PetscObjectParameterSetDefault(snes, max_its, 50);
    1787:   PetscObjectParameterSetDefault(snes, max_funcs, 10000);
    1788:   PetscObjectParameterSetDefault(snes, rtol, PetscDefined(USE_REAL_SINGLE) ? 1.e-5 : 1.e-8);
    1789:   PetscObjectParameterSetDefault(snes, abstol, PetscDefined(USE_REAL_SINGLE) ? 1.e-25 : 1.e-50);
    1790:   PetscObjectParameterSetDefault(snes, stol, PetscDefined(USE_REAL_SINGLE) ? 1.e-5 : 1.e-8);
    1791:   PetscObjectParameterSetDefault(snes, divtol, 1.e4);
    1792:   return PETSC_SUCCESS;
    1793: }

    1795: /*@
    1796:   SNESCreate - Creates a nonlinear solver context used to manage a set of nonlinear solves

    1798:   Collective

    1800:   Input Parameter:
    1801: . comm - MPI communicator

    1803:   Output Parameter:
    1804: . outsnes - the new `SNES` context

    1806:   Options Database Keys:
    1807: + -snes_mf          - Activates default matrix-free Jacobian-vector products, and no preconditioning matrix
    1808: . -snes_mf_operator - Activates default matrix-free Jacobian-vector products, and a user-provided preconditioning matrix
    1809:                       as set by `SNESSetJacobian()`
    1810: . -snes_fd_coloring - uses a relative fast computation of the Jacobian using finite differences and a graph coloring
    1811: - -snes_fd          - Uses (slow!) finite differences to compute Jacobian

    1813:   Level: beginner

    1815:   Developer Notes:
    1816:   `SNES` always creates a `KSP` object even though many `SNES` methods do not use it. This is
    1817:   unfortunate and should be fixed at some point. The flag snes->usesksp indicates if the
    1818:   particular method does use `KSP` and regulates if the information about the `KSP` is printed
    1819:   in `SNESView()`.

    1821:   `TSSetFromOptions()` does call `SNESSetFromOptions()` which can lead to users being confused
    1822:   by help messages about meaningless `SNES` options.

    1824:   `SNES` always creates the snes->kspconvctx even though it is used by only one type. This should be fixed.

    1826: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESDestroy()`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobian()`
    1827: @*/
    1828: PetscErrorCode SNESCreate(MPI_Comm comm, SNES *outsnes)
    1829: {
    1830:   SNES       snes;
    1831:   SNESKSPEW *kctx;

    1833:   PetscFunctionBegin;
    1834:   PetscAssertPointer(outsnes, 2);
    1835:   PetscCall(SNESInitializePackage());

    1837:   PetscCall(PetscHeaderCreate(snes, SNES_CLASSID, "SNES", "Nonlinear solver", "SNES", comm, SNESDestroy, SNESView));
    1838:   snes->ops->converged = SNESConvergedDefault;
    1839:   snes->usesksp        = PETSC_TRUE;
    1840:   snes->norm           = 0.0;
    1841:   snes->xnorm          = 0.0;
    1842:   snes->ynorm          = 0.0;
    1843:   snes->normschedule   = SNES_NORM_ALWAYS;
    1844:   snes->functype       = SNES_FUNCTION_DEFAULT;
    1845:   snes->ttol           = 0.0;

    1847:   snes->rnorm0               = 0;
    1848:   snes->nfuncs               = 0;
    1849:   snes->numFailures          = 0;
    1850:   snes->maxFailures          = 1;
    1851:   snes->linear_its           = 0;
    1852:   snes->lagjacobian          = 1;
    1853:   snes->jac_iter             = 0;
    1854:   snes->lagjac_persist       = PETSC_FALSE;
    1855:   snes->lagpreconditioner    = 1;
    1856:   snes->pre_iter             = 0;
    1857:   snes->lagpre_persist       = PETSC_FALSE;
    1858:   snes->numbermonitors       = 0;
    1859:   snes->numberreasonviews    = 0;
    1860:   snes->data                 = NULL;
    1861:   snes->setupcalled          = PETSC_FALSE;
    1862:   snes->ksp_ewconv           = PETSC_FALSE;
    1863:   snes->nwork                = 0;
    1864:   snes->work                 = NULL;
    1865:   snes->nvwork               = 0;
    1866:   snes->vwork                = NULL;
    1867:   snes->conv_hist_len        = 0;
    1868:   snes->conv_hist_max        = 0;
    1869:   snes->conv_hist            = NULL;
    1870:   snes->conv_hist_its        = NULL;
    1871:   snes->conv_hist_reset      = PETSC_TRUE;
    1872:   snes->counters_reset       = PETSC_TRUE;
    1873:   snes->vec_func_init_set    = PETSC_FALSE;
    1874:   snes->reason               = SNES_CONVERGED_ITERATING;
    1875:   snes->npcside              = PC_RIGHT;
    1876:   snes->setfromoptionscalled = 0;

    1878:   snes->mf          = PETSC_FALSE;
    1879:   snes->mf_operator = PETSC_FALSE;
    1880:   snes->mf_version  = 1;

    1882:   snes->numLinearSolveFailures = 0;
    1883:   snes->maxLinearSolveFailures = 1;

    1885:   snes->vizerotolerance     = 1.e-8;
    1886:   snes->checkjacdomainerror = PetscDefined(USE_DEBUG) ? PETSC_TRUE : PETSC_FALSE;

    1888:   /* Set this to true if the implementation of SNESSolve_XXX does compute the residual at the final solution. */
    1889:   snes->alwayscomputesfinalresidual = PETSC_FALSE;

    1891:   /* Create context to compute Eisenstat-Walker relative tolerance for KSP */
    1892:   PetscCall(PetscNew(&kctx));

    1894:   snes->kspconvctx  = kctx;
    1895:   kctx->version     = 2;
    1896:   kctx->rtol_0      = 0.3; /* Eisenstat and Walker suggest rtol_0=.5, but
    1897:                              this was too large for some test cases */
    1898:   kctx->rtol_last   = 0.0;
    1899:   kctx->rtol_max    = 0.9;
    1900:   kctx->gamma       = 1.0;
    1901:   kctx->alpha       = 0.5 * (1.0 + PetscSqrtReal(5.0));
    1902:   kctx->alpha2      = kctx->alpha;
    1903:   kctx->threshold   = 0.1;
    1904:   kctx->lresid_last = 0.0;
    1905:   kctx->norm_last   = 0.0;

    1907:   kctx->rk_last     = 0.0;
    1908:   kctx->rk_last_2   = 0.0;
    1909:   kctx->rtol_last_2 = 0.0;
    1910:   kctx->v4_p1       = 0.1;
    1911:   kctx->v4_p2       = 0.4;
    1912:   kctx->v4_p3       = 0.7;
    1913:   kctx->v4_m1       = 0.8;
    1914:   kctx->v4_m2       = 0.5;
    1915:   kctx->v4_m3       = 0.1;
    1916:   kctx->v4_m4       = 0.5;

    1918:   PetscCall(SNESParametersInitialize(snes));
    1919:   *outsnes = snes;
    1920:   PetscFunctionReturn(PETSC_SUCCESS);
    1921: }

    1923: /*@C
    1924:   SNESSetFunction - Sets the function evaluation routine and function
    1925:   vector for use by the `SNES` routines in solving systems of nonlinear
    1926:   equations.

    1928:   Logically Collective

    1930:   Input Parameters:
    1931: + snes - the `SNES` context
    1932: . r    - vector to store function values, may be `NULL`
    1933: . f    - function evaluation routine;  for calling sequence see `SNESFunctionFn`
    1934: - ctx  - [optional] user-defined context for private data for the
    1935:          function evaluation routine (may be `NULL`)

    1937:   Level: beginner

    1939: .seealso: [](ch_snes), `SNES`, `SNESGetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESSetPicard()`, `SNESFunctionFn`
    1940: @*/
    1941: PetscErrorCode SNESSetFunction(SNES snes, Vec r, SNESFunctionFn *f, void *ctx)
    1942: {
    1943:   DM dm;

    1945:   PetscFunctionBegin;
    1947:   if (r) {
    1949:     PetscCheckSameComm(snes, 1, r, 2);
    1950:     PetscCall(PetscObjectReference((PetscObject)r));
    1951:     PetscCall(VecDestroy(&snes->vec_func));
    1952:     snes->vec_func = r;
    1953:   }
    1954:   PetscCall(SNESGetDM(snes, &dm));
    1955:   PetscCall(DMSNESSetFunction(dm, f, ctx));
    1956:   if (f == SNESPicardComputeFunction) PetscCall(DMSNESSetMFFunction(dm, SNESPicardComputeMFFunction, ctx));
    1957:   PetscFunctionReturn(PETSC_SUCCESS);
    1958: }

    1960: /*@C
    1961:   SNESSetInitialFunction - Set an already computed function evaluation at the initial guess to be reused by `SNESSolve()`.

    1963:   Logically Collective

    1965:   Input Parameters:
    1966: + snes - the `SNES` context
    1967: - f    - vector to store function value

    1969:   Level: developer

    1971:   Notes:
    1972:   This should not be modified during the solution procedure.

    1974:   This is used extensively in the `SNESFAS` hierarchy and in nonlinear preconditioning.

    1976: .seealso: [](ch_snes), `SNES`, `SNESFAS`, `SNESSetFunction()`, `SNESComputeFunction()`, `SNESSetInitialFunctionNorm()`
    1977: @*/
    1978: PetscErrorCode SNESSetInitialFunction(SNES snes, Vec f)
    1979: {
    1980:   Vec vec_func;

    1982:   PetscFunctionBegin;
    1985:   PetscCheckSameComm(snes, 1, f, 2);
    1986:   if (snes->npcside == PC_LEFT && snes->functype == SNES_FUNCTION_PRECONDITIONED) {
    1987:     snes->vec_func_init_set = PETSC_FALSE;
    1988:     PetscFunctionReturn(PETSC_SUCCESS);
    1989:   }
    1990:   PetscCall(SNESGetFunction(snes, &vec_func, NULL, NULL));
    1991:   PetscCall(VecCopy(f, vec_func));

    1993:   snes->vec_func_init_set = PETSC_TRUE;
    1994:   PetscFunctionReturn(PETSC_SUCCESS);
    1995: }

    1997: /*@
    1998:   SNESSetNormSchedule - Sets the `SNESNormSchedule` used in convergence and monitoring
    1999:   of the `SNES` method, when norms are computed in the solving process

    2001:   Logically Collective

    2003:   Input Parameters:
    2004: + snes         - the `SNES` context
    2005: - normschedule - the frequency of norm computation

    2007:   Options Database Key:
    2008: . -snes_norm_schedule <none, always, initialonly, finalonly, initialfinalonly> - set the schedule

    2010:   Level: advanced

    2012:   Notes:
    2013:   Only certain `SNES` methods support certain `SNESNormSchedules`.  Most require evaluation
    2014:   of the nonlinear function and the taking of its norm at every iteration to
    2015:   even ensure convergence at all.  However, methods such as custom Gauss-Seidel methods
    2016:   `SNESNGS` and the like do not require the norm of the function to be computed, and therefore
    2017:   may either be monitored for convergence or not.  As these are often used as nonlinear
    2018:   preconditioners, monitoring the norm of their error is not a useful enterprise within
    2019:   their solution.

    2021: .seealso: [](ch_snes), `SNESNormSchedule`, `SNESGetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`
    2022: @*/
    2023: PetscErrorCode SNESSetNormSchedule(SNES snes, SNESNormSchedule normschedule)
    2024: {
    2025:   PetscFunctionBegin;
    2027:   snes->normschedule = normschedule;
    2028:   PetscFunctionReturn(PETSC_SUCCESS);
    2029: }

    2031: /*@
    2032:   SNESGetNormSchedule - Gets the `SNESNormSchedule` used in convergence and monitoring
    2033:   of the `SNES` method.

    2035:   Logically Collective

    2037:   Input Parameters:
    2038: + snes         - the `SNES` context
    2039: - normschedule - the type of the norm used

    2041:   Level: advanced

    2043: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2044: @*/
    2045: PetscErrorCode SNESGetNormSchedule(SNES snes, SNESNormSchedule *normschedule)
    2046: {
    2047:   PetscFunctionBegin;
    2049:   *normschedule = snes->normschedule;
    2050:   PetscFunctionReturn(PETSC_SUCCESS);
    2051: }

    2053: /*@
    2054:   SNESSetFunctionNorm - Sets the last computed residual norm.

    2056:   Logically Collective

    2058:   Input Parameters:
    2059: + snes - the `SNES` context
    2060: - norm - the value of the norm

    2062:   Level: developer

    2064: .seealso: [](ch_snes), `SNES`, `SNESGetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2065: @*/
    2066: PetscErrorCode SNESSetFunctionNorm(SNES snes, PetscReal norm)
    2067: {
    2068:   PetscFunctionBegin;
    2070:   snes->norm = norm;
    2071:   PetscFunctionReturn(PETSC_SUCCESS);
    2072: }

    2074: /*@
    2075:   SNESGetFunctionNorm - Gets the last computed norm of the residual

    2077:   Not Collective

    2079:   Input Parameter:
    2080: . snes - the `SNES` context

    2082:   Output Parameter:
    2083: . norm - the last computed residual norm

    2085:   Level: developer

    2087: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2088: @*/
    2089: PetscErrorCode SNESGetFunctionNorm(SNES snes, PetscReal *norm)
    2090: {
    2091:   PetscFunctionBegin;
    2093:   PetscAssertPointer(norm, 2);
    2094:   *norm = snes->norm;
    2095:   PetscFunctionReturn(PETSC_SUCCESS);
    2096: }

    2098: /*@
    2099:   SNESGetUpdateNorm - Gets the last computed norm of the solution update

    2101:   Not Collective

    2103:   Input Parameter:
    2104: . snes - the `SNES` context

    2106:   Output Parameter:
    2107: . ynorm - the last computed update norm

    2109:   Level: developer

    2111:   Note:
    2112:   The new solution is the current solution plus the update, so this norm is an indication of the size of the update

    2114: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `SNESGetFunctionNorm()`
    2115: @*/
    2116: PetscErrorCode SNESGetUpdateNorm(SNES snes, PetscReal *ynorm)
    2117: {
    2118:   PetscFunctionBegin;
    2120:   PetscAssertPointer(ynorm, 2);
    2121:   *ynorm = snes->ynorm;
    2122:   PetscFunctionReturn(PETSC_SUCCESS);
    2123: }

    2125: /*@
    2126:   SNESGetSolutionNorm - Gets the last computed norm of the solution

    2128:   Not Collective

    2130:   Input Parameter:
    2131: . snes - the `SNES` context

    2133:   Output Parameter:
    2134: . xnorm - the last computed solution norm

    2136:   Level: developer

    2138: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `SNESGetFunctionNorm()`, `SNESGetUpdateNorm()`
    2139: @*/
    2140: PetscErrorCode SNESGetSolutionNorm(SNES snes, PetscReal *xnorm)
    2141: {
    2142:   PetscFunctionBegin;
    2144:   PetscAssertPointer(xnorm, 2);
    2145:   *xnorm = snes->xnorm;
    2146:   PetscFunctionReturn(PETSC_SUCCESS);
    2147: }

    2149: /*@
    2150:   SNESSetFunctionType - Sets the `SNESFunctionType`
    2151:   of the `SNES` method.

    2153:   Logically Collective

    2155:   Input Parameters:
    2156: + snes - the `SNES` context
    2157: - type - the function type

    2159:   Level: developer

    2161:   Values of the function type\:
    2162: +  `SNES_FUNCTION_DEFAULT`          - the default for the given `SNESType`
    2163: .  `SNES_FUNCTION_UNPRECONDITIONED` - an unpreconditioned function evaluation (this is the function provided with `SNESSetFunction()`
    2164: -  `SNES_FUNCTION_PRECONDITIONED`   - a transformation of the function provided with `SNESSetFunction()`

    2166:   Note:
    2167:   Different `SNESType`s use this value in different ways

    2169: .seealso: [](ch_snes), `SNES`, `SNESFunctionType`, `SNESGetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2170: @*/
    2171: PetscErrorCode SNESSetFunctionType(SNES snes, SNESFunctionType type)
    2172: {
    2173:   PetscFunctionBegin;
    2175:   snes->functype = type;
    2176:   PetscFunctionReturn(PETSC_SUCCESS);
    2177: }

    2179: /*@
    2180:   SNESGetFunctionType - Gets the `SNESFunctionType` used in convergence and monitoring set with `SNESSetFunctionType()`
    2181:   of the SNES method.

    2183:   Logically Collective

    2185:   Input Parameters:
    2186: + snes - the `SNES` context
    2187: - type - the type of the function evaluation, see `SNESSetFunctionType()`

    2189:   Level: advanced

    2191: .seealso: [](ch_snes), `SNESSetFunctionType()`, `SNESFunctionType`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2192: @*/
    2193: PetscErrorCode SNESGetFunctionType(SNES snes, SNESFunctionType *type)
    2194: {
    2195:   PetscFunctionBegin;
    2197:   *type = snes->functype;
    2198:   PetscFunctionReturn(PETSC_SUCCESS);
    2199: }

    2201: /*@C
    2202:   SNESSetNGS - Sets the user nonlinear Gauss-Seidel routine for
    2203:   use with composed nonlinear solvers.

    2205:   Input Parameters:
    2206: + snes - the `SNES` context, usually of the `SNESType` `SNESNGS`
    2207: . f    - function evaluation routine to apply Gauss-Seidel, see `SNESNGSFn` for calling sequence
    2208: - ctx  - [optional] user-defined context for private data for the smoother evaluation routine (may be `NULL`)

    2210:   Level: intermediate

    2212:   Note:
    2213:   The `SNESNGS` routines are used by the composed nonlinear solver to generate
    2214:   a problem appropriate update to the solution, particularly `SNESFAS`.

    2216: .seealso: [](ch_snes), `SNESNGS`, `SNESGetNGS()`, `SNESNCG`, `SNESGetFunction()`, `SNESComputeNGS()`, `SNESNGSFn`
    2217: @*/
    2218: PetscErrorCode SNESSetNGS(SNES snes, SNESNGSFn *f, void *ctx)
    2219: {
    2220:   DM dm;

    2222:   PetscFunctionBegin;
    2224:   PetscCall(SNESGetDM(snes, &dm));
    2225:   PetscCall(DMSNESSetNGS(dm, f, ctx));
    2226:   PetscFunctionReturn(PETSC_SUCCESS);
    2227: }

    2229: /*
    2230:      This is used for -snes_mf_operator; it uses a duplicate of snes->jacobian_pre because snes->jacobian_pre cannot be
    2231:    changed during the KSPSolve()
    2232: */
    2233: PetscErrorCode SNESPicardComputeMFFunction(SNES snes, Vec x, Vec f, void *ctx)
    2234: {
    2235:   DM     dm;
    2236:   DMSNES sdm;

    2238:   PetscFunctionBegin;
    2239:   PetscCall(SNESGetDM(snes, &dm));
    2240:   PetscCall(DMGetDMSNES(dm, &sdm));
    2241:   /*  A(x)*x - b(x) */
    2242:   if (sdm->ops->computepfunction) {
    2243:     PetscCallBack("SNES Picard callback function", (*sdm->ops->computepfunction)(snes, x, f, sdm->pctx));
    2244:     PetscCall(VecScale(f, -1.0));
    2245:     /* Cannot share nonzero pattern because of the possible use of SNESComputeJacobianDefault() */
    2246:     if (!snes->picard) PetscCall(MatDuplicate(snes->jacobian_pre, MAT_DO_NOT_COPY_VALUES, &snes->picard));
    2247:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->picard, snes->picard, sdm->pctx));
    2248:     PetscCall(MatMultAdd(snes->picard, x, f, f));
    2249:   } else {
    2250:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->picard, snes->picard, sdm->pctx));
    2251:     PetscCall(MatMult(snes->picard, x, f));
    2252:   }
    2253:   PetscFunctionReturn(PETSC_SUCCESS);
    2254: }

    2256: PetscErrorCode SNESPicardComputeFunction(SNES snes, Vec x, Vec f, void *ctx)
    2257: {
    2258:   DM     dm;
    2259:   DMSNES sdm;

    2261:   PetscFunctionBegin;
    2262:   PetscCall(SNESGetDM(snes, &dm));
    2263:   PetscCall(DMGetDMSNES(dm, &sdm));
    2264:   /*  A(x)*x - b(x) */
    2265:   if (sdm->ops->computepfunction) {
    2266:     PetscCallBack("SNES Picard callback function", (*sdm->ops->computepfunction)(snes, x, f, sdm->pctx));
    2267:     PetscCall(VecScale(f, -1.0));
    2268:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->jacobian, snes->jacobian_pre, sdm->pctx));
    2269:     PetscCall(MatMultAdd(snes->jacobian_pre, x, f, f));
    2270:   } else {
    2271:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->jacobian, snes->jacobian_pre, sdm->pctx));
    2272:     PetscCall(MatMult(snes->jacobian_pre, x, f));
    2273:   }
    2274:   PetscFunctionReturn(PETSC_SUCCESS);
    2275: }

    2277: PetscErrorCode SNESPicardComputeJacobian(SNES snes, Vec x1, Mat J, Mat B, void *ctx)
    2278: {
    2279:   PetscFunctionBegin;
    2280:   /* the jacobian matrix should be pre-filled in SNESPicardComputeFunction */
    2281:   /* must assembly if matrix-free to get the last SNES solution */
    2282:   PetscCall(MatAssemblyBegin(J, MAT_FINAL_ASSEMBLY));
    2283:   PetscCall(MatAssemblyEnd(J, MAT_FINAL_ASSEMBLY));
    2284:   PetscFunctionReturn(PETSC_SUCCESS);
    2285: }

    2287: /*@C
    2288:   SNESSetPicard - Use `SNES` to solve the system $A(x) x = bp(x) + b $ via a Picard type iteration (Picard linearization)

    2290:   Logically Collective

    2292:   Input Parameters:
    2293: + snes - the `SNES` context
    2294: . r    - vector to store function values, may be `NULL`
    2295: . bp   - function evaluation routine, may be `NULL`, for the calling sequence see `SNESFunctionFn`
    2296: . Amat - matrix with which $A(x) x - bp(x) - b$ is to be computed
    2297: . Pmat - matrix from which preconditioner is computed (usually the same as `Amat`)
    2298: . J    - function to compute matrix values, for the calling sequence see `SNESJacobianFn`
    2299: - ctx  - [optional] user-defined context for private data for the function evaluation routine (may be `NULL`)

    2301:   Level: intermediate

    2303:   Notes:
    2304:   It is often better to provide the nonlinear function $F()$ and some approximation to its Jacobian directly and use
    2305:   an approximate Newton solver. This interface is provided to allow porting/testing a previous Picard based code in PETSc before converting it to approximate Newton.

    2307:   One can call `SNESSetPicard()` or `SNESSetFunction()` (and possibly `SNESSetJacobian()`) but cannot call both

    2309:   Solves the equation $A(x) x = bp(x) - b$ via the defect correction algorithm $A(x^{n}) (x^{n+1} - x^{n}) = bp(x^{n}) + b - A(x^{n})x^{n}$.
    2310:   When an exact solver is used this corresponds to the "classic" Picard $A(x^{n}) x^{n+1} = bp(x^{n}) + b$ iteration.

    2312:   Run with `-snes_mf_operator` to solve the system with Newton's method using $A(x^{n})$ to construct the preconditioner.

    2314:   We implement the defect correction form of the Picard iteration because it converges much more generally when inexact linear solvers are used then
    2315:   the direct Picard iteration $A(x^n) x^{n+1} = bp(x^n) + b$

    2317:   There is some controversity over the definition of a Picard iteration for nonlinear systems but almost everyone agrees that it involves a linear solve and some
    2318:   believe it is the iteration  $A(x^{n}) x^{n+1} = b(x^{n})$ hence we use the name Picard. If anyone has an authoritative  reference that defines the Picard iteration
    2319:   different please contact us at petsc-dev@mcs.anl.gov and we'll have an entirely new argument \:-).

    2321:   When used with `-snes_mf_operator` this will run matrix-free Newton's method where the matrix-vector product is of the true Jacobian of $A(x)x - bp(x) - b$ and
    2322:   $A(x^{n})$ is used to build the preconditioner

    2324:   When used with `-snes_fd` this will compute the true Jacobian (very slowly one column at a time) and thus represent Newton's method.

    2326:   When used with `-snes_fd_coloring` this will compute the Jacobian via coloring and thus represent a faster implementation of Newton's method. But the
    2327:   the nonzero structure of the Jacobian is, in general larger than that of the Picard matrix $A$ so you must provide in $A$ the needed nonzero structure for the correct
    2328:   coloring. When using `DMDA` this may mean creating the matrix $A$ with `DMCreateMatrix()` using a wider stencil than strictly needed for $A$ or with a `DMDA_STENCIL_BOX`.
    2329:   See the comment in src/snes/tutorials/ex15.c.

    2331: .seealso: [](ch_snes), `SNES`, `SNESGetFunction()`, `SNESSetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESGetPicard()`, `SNESLineSearchPreCheckPicard()`,
    2332:           `SNESFunctionFn`, `SNESJacobianFn`
    2333: @*/
    2334: PetscErrorCode SNESSetPicard(SNES snes, Vec r, SNESFunctionFn *bp, Mat Amat, Mat Pmat, SNESJacobianFn *J, void *ctx)
    2335: {
    2336:   DM dm;

    2338:   PetscFunctionBegin;
    2340:   PetscCall(SNESGetDM(snes, &dm));
    2341:   PetscCall(DMSNESSetPicard(dm, bp, J, ctx));
    2342:   PetscCall(DMSNESSetMFFunction(dm, SNESPicardComputeMFFunction, ctx));
    2343:   PetscCall(SNESSetFunction(snes, r, SNESPicardComputeFunction, ctx));
    2344:   PetscCall(SNESSetJacobian(snes, Amat, Pmat, SNESPicardComputeJacobian, ctx));
    2345:   PetscFunctionReturn(PETSC_SUCCESS);
    2346: }

    2348: /*@C
    2349:   SNESGetPicard - Returns the context for the Picard iteration

    2351:   Not Collective, but `Vec` is parallel if `SNES` is parallel. Collective if `Vec` is requested, but has not been created yet.

    2353:   Input Parameter:
    2354: . snes - the `SNES` context

    2356:   Output Parameters:
    2357: + r    - the function (or `NULL`)
    2358: . f    - the function (or `NULL`);  for calling sequence see `SNESFunctionFn`
    2359: . Amat - the matrix used to defined the operation A(x) x - b(x) (or `NULL`)
    2360: . Pmat - the matrix from which the preconditioner will be constructed (or `NULL`)
    2361: . J    - the function for matrix evaluation (or `NULL`);  for calling sequence see `SNESJacobianFn`
    2362: - ctx  - the function context (or `NULL`)

    2364:   Level: advanced

    2366: .seealso: [](ch_snes), `SNESSetFunction()`, `SNESSetPicard()`, `SNESGetFunction()`, `SNESGetJacobian()`, `SNESGetDM()`, `SNESFunctionFn`, `SNESJacobianFn`
    2367: @*/
    2368: PetscErrorCode SNESGetPicard(SNES snes, Vec *r, SNESFunctionFn **f, Mat *Amat, Mat *Pmat, SNESJacobianFn **J, void **ctx)
    2369: {
    2370:   DM dm;

    2372:   PetscFunctionBegin;
    2374:   PetscCall(SNESGetFunction(snes, r, NULL, NULL));
    2375:   PetscCall(SNESGetJacobian(snes, Amat, Pmat, NULL, NULL));
    2376:   PetscCall(SNESGetDM(snes, &dm));
    2377:   PetscCall(DMSNESGetPicard(dm, f, J, ctx));
    2378:   PetscFunctionReturn(PETSC_SUCCESS);
    2379: }

    2381: /*@C
    2382:   SNESSetComputeInitialGuess - Sets a routine used to compute an initial guess for the nonlinear problem

    2384:   Logically Collective

    2386:   Input Parameters:
    2387: + snes - the `SNES` context
    2388: . func - function evaluation routine, see `SNESInitialGuessFn` for the calling sequence
    2389: - ctx  - [optional] user-defined context for private data for the
    2390:          function evaluation routine (may be `NULL`)

    2392:   Level: intermediate

    2394: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetFunction()`, `SNESGetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESInitialGuessFn`
    2395: @*/
    2396: PetscErrorCode SNESSetComputeInitialGuess(SNES snes, SNESInitialGuessFn *func, void *ctx)
    2397: {
    2398:   PetscFunctionBegin;
    2400:   if (func) snes->ops->computeinitialguess = func;
    2401:   if (ctx) snes->initialguessP = ctx;
    2402:   PetscFunctionReturn(PETSC_SUCCESS);
    2403: }

    2405: /*@C
    2406:   SNESGetRhs - Gets the vector for solving F(x) = `rhs`. If `rhs` is not set
    2407:   it assumes a zero right-hand side.

    2409:   Logically Collective

    2411:   Input Parameter:
    2412: . snes - the `SNES` context

    2414:   Output Parameter:
    2415: . rhs - the right-hand side vector or `NULL` if there is no right-hand side vector

    2417:   Level: intermediate

    2419: .seealso: [](ch_snes), `SNES`, `SNESGetSolution()`, `SNESGetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESSetFunction()`
    2420: @*/
    2421: PetscErrorCode SNESGetRhs(SNES snes, Vec *rhs)
    2422: {
    2423:   PetscFunctionBegin;
    2425:   PetscAssertPointer(rhs, 2);
    2426:   *rhs = snes->vec_rhs;
    2427:   PetscFunctionReturn(PETSC_SUCCESS);
    2428: }

    2430: /*@
    2431:   SNESComputeFunction - Calls the function that has been set with `SNESSetFunction()`.

    2433:   Collective

    2435:   Input Parameters:
    2436: + snes - the `SNES` context
    2437: - x    - input vector

    2439:   Output Parameter:
    2440: . y - function vector, as set by `SNESSetFunction()`

    2442:   Level: developer

    2444:   Notes:
    2445:   `SNESComputeFunction()` is typically used within nonlinear solvers
    2446:   implementations, so users would not generally call this routine themselves.

    2448:   When solving for $F(x) = b$, this routine computes $y = F(x) - b$.

    2450: .seealso: [](ch_snes), `SNES`, `SNESSetFunction()`, `SNESGetFunction()`, `SNESComputeMFFunction()`
    2451: @*/
    2452: PetscErrorCode SNESComputeFunction(SNES snes, Vec x, Vec y)
    2453: {
    2454:   DM     dm;
    2455:   DMSNES sdm;

    2457:   PetscFunctionBegin;
    2461:   PetscCheckSameComm(snes, 1, x, 2);
    2462:   PetscCheckSameComm(snes, 1, y, 3);
    2463:   PetscCall(VecValidValues_Internal(x, 2, PETSC_TRUE));

    2465:   PetscCall(SNESGetDM(snes, &dm));
    2466:   PetscCall(DMGetDMSNES(dm, &sdm));
    2467:   PetscCheck(sdm->ops->computefunction || snes->vec_rhs, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Must call SNESSetFunction() or SNESSetDM() before SNESComputeFunction(), likely called from SNESSolve().");
    2468:   if (sdm->ops->computefunction) {
    2469:     if (sdm->ops->computefunction != SNESObjectiveComputeFunctionDefaultFD) PetscCall(PetscLogEventBegin(SNES_FunctionEval, snes, x, y, 0));
    2470:     PetscCall(VecLockReadPush(x));
    2471:     /* ensure domainerror is false prior to computefunction evaluation (may not have been reset) */
    2472:     snes->domainerror = PETSC_FALSE;
    2473:     {
    2474:       void           *ctx;
    2475:       SNESFunctionFn *computefunction;
    2476:       PetscCall(DMSNESGetFunction(dm, &computefunction, &ctx));
    2477:       PetscCallBack("SNES callback function", (*computefunction)(snes, x, y, ctx));
    2478:     }
    2479:     PetscCall(VecLockReadPop(x));
    2480:     if (sdm->ops->computefunction != SNESObjectiveComputeFunctionDefaultFD) PetscCall(PetscLogEventEnd(SNES_FunctionEval, snes, x, y, 0));
    2481:   } else /* if (snes->vec_rhs) */ {
    2482:     PetscCall(MatMult(snes->jacobian, x, y));
    2483:   }
    2484:   if (snes->vec_rhs) PetscCall(VecAXPY(y, -1.0, snes->vec_rhs));
    2485:   snes->nfuncs++;
    2486:   /*
    2487:      domainerror might not be set on all processes; so we tag vector locally with Inf and the next inner product or norm will
    2488:      propagate the value to all processes
    2489:   */
    2490:   PetscCall(VecFlag(y, snes->domainerror));
    2491:   PetscFunctionReturn(PETSC_SUCCESS);
    2492: }

    2494: /*@
    2495:   SNESComputeMFFunction - Calls the function that has been set with `DMSNESSetMFFunction()`.

    2497:   Collective

    2499:   Input Parameters:
    2500: + snes - the `SNES` context
    2501: - x    - input vector

    2503:   Output Parameter:
    2504: . y - output vector

    2506:   Level: developer

    2508:   Notes:
    2509:   `SNESComputeMFFunction()` is used within the matrix-vector products called by the matrix created with `MatCreateSNESMF()`
    2510:   so users would not generally call this routine themselves.

    2512:   Since this function is intended for use with finite differencing it does not subtract the right-hand side vector provided with `SNESSolve()`
    2513:   while `SNESComputeFunction()` does. As such, this routine cannot be used with  `MatMFFDSetBase()` with a provided F function value even if it applies the
    2514:   same function as `SNESComputeFunction()` if a `SNESSolve()` right-hand side vector is use because the two functions difference would include this right hand side function.

    2516: .seealso: [](ch_snes), `SNES`, `SNESSetFunction()`, `SNESGetFunction()`, `SNESComputeFunction()`, `MatCreateSNESMF()`, `DMSNESSetMFFunction()`
    2517: @*/
    2518: PetscErrorCode SNESComputeMFFunction(SNES snes, Vec x, Vec y)
    2519: {
    2520:   DM     dm;
    2521:   DMSNES sdm;

    2523:   PetscFunctionBegin;
    2527:   PetscCheckSameComm(snes, 1, x, 2);
    2528:   PetscCheckSameComm(snes, 1, y, 3);
    2529:   PetscCall(VecValidValues_Internal(x, 2, PETSC_TRUE));

    2531:   PetscCall(SNESGetDM(snes, &dm));
    2532:   PetscCall(DMGetDMSNES(dm, &sdm));
    2533:   PetscCall(PetscLogEventBegin(SNES_FunctionEval, snes, x, y, 0));
    2534:   PetscCall(VecLockReadPush(x));
    2535:   /* ensure domainerror is false prior to computefunction evaluation (may not have been reset) */
    2536:   snes->domainerror = PETSC_FALSE;
    2537:   PetscCallBack("SNES callback function", (*sdm->ops->computemffunction)(snes, x, y, sdm->mffunctionctx));
    2538:   PetscCall(VecLockReadPop(x));
    2539:   PetscCall(PetscLogEventEnd(SNES_FunctionEval, snes, x, y, 0));
    2540:   snes->nfuncs++;
    2541:   /*
    2542:      domainerror might not be set on all processes; so we tag vector locally with Inf and the next inner product or norm will
    2543:      propagate the value to all processes
    2544:   */
    2545:   PetscCall(VecFlag(y, snes->domainerror));
    2546:   PetscFunctionReturn(PETSC_SUCCESS);
    2547: }

    2549: /*@
    2550:   SNESComputeNGS - Calls the Gauss-Seidel function that has been set with `SNESSetNGS()`.

    2552:   Collective

    2554:   Input Parameters:
    2555: + snes - the `SNES` context
    2556: . x    - input vector
    2557: - b    - rhs vector

    2559:   Output Parameter:
    2560: . x - new solution vector

    2562:   Level: developer

    2564:   Note:
    2565:   `SNESComputeNGS()` is typically used within composed nonlinear solver
    2566:   implementations, so most users would not generally call this routine
    2567:   themselves.

    2569: .seealso: [](ch_snes), `SNESNGSFn`, `SNESSetNGS()`, `SNESComputeFunction()`, `SNESNGS`
    2570: @*/
    2571: PetscErrorCode SNESComputeNGS(SNES snes, Vec b, Vec x)
    2572: {
    2573:   DM     dm;
    2574:   DMSNES sdm;

    2576:   PetscFunctionBegin;
    2580:   PetscCheckSameComm(snes, 1, x, 3);
    2581:   if (b) PetscCheckSameComm(snes, 1, b, 2);
    2582:   if (b) PetscCall(VecValidValues_Internal(b, 2, PETSC_TRUE));
    2583:   PetscCall(PetscLogEventBegin(SNES_NGSEval, snes, x, b, 0));
    2584:   PetscCall(SNESGetDM(snes, &dm));
    2585:   PetscCall(DMGetDMSNES(dm, &sdm));
    2586:   PetscCheck(sdm->ops->computegs, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Must call SNESSetNGS() before SNESComputeNGS(), likely called from SNESSolve().");
    2587:   if (b) PetscCall(VecLockReadPush(b));
    2588:   PetscCallBack("SNES callback NGS", (*sdm->ops->computegs)(snes, x, b, sdm->gsctx));
    2589:   if (b) PetscCall(VecLockReadPop(b));
    2590:   PetscCall(PetscLogEventEnd(SNES_NGSEval, snes, x, b, 0));
    2591:   PetscFunctionReturn(PETSC_SUCCESS);
    2592: }

    2594: static PetscErrorCode SNESComputeFunction_FD(SNES snes, Vec Xin, Vec G)
    2595: {
    2596:   Vec          X;
    2597:   PetscScalar *g;
    2598:   PetscReal    f, f2;
    2599:   PetscInt     low, high, N, i;
    2600:   PetscBool    flg;
    2601:   PetscReal    h = .5 * PETSC_SQRT_MACHINE_EPSILON;

    2603:   PetscFunctionBegin;
    2604:   PetscCall(PetscOptionsGetReal(((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_fd_delta", &h, &flg));
    2605:   PetscCall(VecDuplicate(Xin, &X));
    2606:   PetscCall(VecCopy(Xin, X));
    2607:   PetscCall(VecGetSize(X, &N));
    2608:   PetscCall(VecGetOwnershipRange(X, &low, &high));
    2609:   PetscCall(VecSetOption(X, VEC_IGNORE_OFF_PROC_ENTRIES, PETSC_TRUE));
    2610:   PetscCall(VecGetArray(G, &g));
    2611:   for (i = 0; i < N; i++) {
    2612:     PetscCall(VecSetValue(X, i, -h, ADD_VALUES));
    2613:     PetscCall(VecAssemblyBegin(X));
    2614:     PetscCall(VecAssemblyEnd(X));
    2615:     PetscCall(SNESComputeObjective(snes, X, &f));
    2616:     PetscCall(VecSetValue(X, i, 2.0 * h, ADD_VALUES));
    2617:     PetscCall(VecAssemblyBegin(X));
    2618:     PetscCall(VecAssemblyEnd(X));
    2619:     PetscCall(SNESComputeObjective(snes, X, &f2));
    2620:     PetscCall(VecSetValue(X, i, -h, ADD_VALUES));
    2621:     PetscCall(VecAssemblyBegin(X));
    2622:     PetscCall(VecAssemblyEnd(X));
    2623:     if (i >= low && i < high) g[i - low] = (f2 - f) / (2.0 * h);
    2624:   }
    2625:   PetscCall(VecRestoreArray(G, &g));
    2626:   PetscCall(VecDestroy(&X));
    2627:   PetscFunctionReturn(PETSC_SUCCESS);
    2628: }

    2630: PetscErrorCode SNESTestFunction(SNES snes)
    2631: {
    2632:   Vec               x, g1, g2, g3;
    2633:   PetscBool         complete_print = PETSC_FALSE, test = PETSC_FALSE;
    2634:   PetscReal         hcnorm, fdnorm, hcmax, fdmax, diffmax, diffnorm;
    2635:   PetscScalar       dot;
    2636:   MPI_Comm          comm;
    2637:   PetscViewer       viewer, mviewer;
    2638:   PetscViewerFormat format;
    2639:   PetscInt          tabs;
    2640:   static PetscBool  directionsprinted = PETSC_FALSE;
    2641:   SNESObjectiveFn  *objective;

    2643:   PetscFunctionBegin;
    2644:   PetscCall(SNESGetObjective(snes, &objective, NULL));
    2645:   if (!objective) PetscFunctionReturn(PETSC_SUCCESS);

    2647:   PetscObjectOptionsBegin((PetscObject)snes);
    2648:   PetscCall(PetscOptionsName("-snes_test_function", "Compare hand-coded and finite difference function", "None", &test));
    2649:   PetscCall(PetscOptionsViewer("-snes_test_function_view", "View difference between hand-coded and finite difference function element entries", "None", &mviewer, &format, &complete_print));
    2650:   PetscOptionsEnd();
    2651:   if (!test) {
    2652:     if (complete_print) PetscCall(PetscViewerDestroy(&mviewer));
    2653:     PetscFunctionReturn(PETSC_SUCCESS);
    2654:   }

    2656:   PetscCall(PetscObjectGetComm((PetscObject)snes, &comm));
    2657:   PetscCall(PetscViewerASCIIGetStdout(comm, &viewer));
    2658:   PetscCall(PetscViewerASCIIGetTab(viewer, &tabs));
    2659:   PetscCall(PetscViewerASCIISetTab(viewer, ((PetscObject)snes)->tablevel));
    2660:   PetscCall(PetscViewerASCIIPrintf(viewer, "  ---------- Testing Function -------------\n"));
    2661:   if (!complete_print && !directionsprinted) {
    2662:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Run with -snes_test_function_view and optionally -snes_test_function <threshold> to show difference\n"));
    2663:     PetscCall(PetscViewerASCIIPrintf(viewer, "    of hand-coded and finite difference function entries greater than <threshold>.\n"));
    2664:   }
    2665:   if (!directionsprinted) {
    2666:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Testing hand-coded Function, if (for double precision runs) ||F - Ffd||/||F|| is\n"));
    2667:     PetscCall(PetscViewerASCIIPrintf(viewer, "    O(1.e-8), the hand-coded Function is probably correct.\n"));
    2668:     directionsprinted = PETSC_TRUE;
    2669:   }
    2670:   if (complete_print) PetscCall(PetscViewerPushFormat(mviewer, format));

    2672:   PetscCall(SNESGetSolution(snes, &x));
    2673:   PetscCall(VecDuplicate(x, &g1));
    2674:   PetscCall(VecDuplicate(x, &g2));
    2675:   PetscCall(VecDuplicate(x, &g3));
    2676:   PetscCall(SNESComputeFunction(snes, x, g1));
    2677:   PetscCall(SNESComputeFunction_FD(snes, x, g2));

    2679:   PetscCall(VecNorm(g2, NORM_2, &fdnorm));
    2680:   PetscCall(VecNorm(g1, NORM_2, &hcnorm));
    2681:   PetscCall(VecNorm(g2, NORM_INFINITY, &fdmax));
    2682:   PetscCall(VecNorm(g1, NORM_INFINITY, &hcmax));
    2683:   PetscCall(VecDot(g1, g2, &dot));
    2684:   PetscCall(VecCopy(g1, g3));
    2685:   PetscCall(VecAXPY(g3, -1.0, g2));
    2686:   PetscCall(VecNorm(g3, NORM_2, &diffnorm));
    2687:   PetscCall(VecNorm(g3, NORM_INFINITY, &diffmax));
    2688:   PetscCall(PetscViewerASCIIPrintf(viewer, "  ||Ffd|| %g, ||F|| = %g, angle cosine = (Ffd'F)/||Ffd||||F|| = %g\n", (double)fdnorm, (double)hcnorm, (double)(PetscRealPart(dot) / (fdnorm * hcnorm))));
    2689:   PetscCall(PetscViewerASCIIPrintf(viewer, "  2-norm ||F - Ffd||/||F|| = %g, ||F - Ffd|| = %g\n", (double)(diffnorm / PetscMax(hcnorm, fdnorm)), (double)diffnorm));
    2690:   PetscCall(PetscViewerASCIIPrintf(viewer, "  max-norm ||F - Ffd||/||F|| = %g, ||F - Ffd|| = %g\n", (double)(diffmax / PetscMax(hcmax, fdmax)), (double)diffmax));

    2692:   if (complete_print) {
    2693:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded function ----------\n"));
    2694:     PetscCall(VecView(g1, mviewer));
    2695:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Finite difference function ----------\n"));
    2696:     PetscCall(VecView(g2, mviewer));
    2697:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded minus finite-difference function ----------\n"));
    2698:     PetscCall(VecView(g3, mviewer));
    2699:   }
    2700:   PetscCall(VecDestroy(&g1));
    2701:   PetscCall(VecDestroy(&g2));
    2702:   PetscCall(VecDestroy(&g3));

    2704:   if (complete_print) {
    2705:     PetscCall(PetscViewerPopFormat(mviewer));
    2706:     PetscCall(PetscViewerDestroy(&mviewer));
    2707:   }
    2708:   PetscCall(PetscViewerASCIISetTab(viewer, tabs));
    2709:   PetscFunctionReturn(PETSC_SUCCESS);
    2710: }

    2712: PetscErrorCode SNESTestJacobian(SNES snes)
    2713: {
    2714:   Mat               A, B, C, D, jacobian;
    2715:   Vec               x = snes->vec_sol, f;
    2716:   PetscReal         nrm, gnorm;
    2717:   PetscReal         threshold = 1.e-5;
    2718:   MatType           mattype;
    2719:   PetscInt          m, n, M, N;
    2720:   void             *functx;
    2721:   PetscBool         complete_print = PETSC_FALSE, threshold_print = PETSC_FALSE, test = PETSC_FALSE, flg, istranspose;
    2722:   PetscViewer       viewer, mviewer;
    2723:   MPI_Comm          comm;
    2724:   PetscInt          tabs;
    2725:   static PetscBool  directionsprinted = PETSC_FALSE;
    2726:   PetscViewerFormat format;

    2728:   PetscFunctionBegin;
    2729:   PetscObjectOptionsBegin((PetscObject)snes);
    2730:   PetscCall(PetscOptionsName("-snes_test_jacobian", "Compare hand-coded and finite difference Jacobians", "None", &test));
    2731:   PetscCall(PetscOptionsReal("-snes_test_jacobian", "Threshold for element difference between hand-coded and finite difference being meaningful", "None", threshold, &threshold, NULL));
    2732:   PetscCall(PetscOptionsDeprecated("-snes_test_jacobian_display", "-snes_test_jacobian_view", "3.13", NULL));
    2733:   PetscCall(PetscOptionsViewer("-snes_test_jacobian_view", "View difference between hand-coded and finite difference Jacobians element entries", "None", &mviewer, &format, &complete_print));
    2734:   PetscCall(PetscOptionsDeprecated("-snes_test_jacobian_display_threshold", "-snes_test_jacobian", "3.13", "-snes_test_jacobian accepts an optional threshold (since v3.10)"));
    2735:   PetscCall(PetscOptionsReal("-snes_test_jacobian_display_threshold", "Display difference between hand-coded and finite difference Jacobians which exceed input threshold", "None", threshold, &threshold, &threshold_print));
    2736:   PetscOptionsEnd();
    2737:   if (!test) PetscFunctionReturn(PETSC_SUCCESS);

    2739:   PetscCall(PetscObjectGetComm((PetscObject)snes, &comm));
    2740:   PetscCall(PetscViewerASCIIGetStdout(comm, &viewer));
    2741:   PetscCall(PetscViewerASCIIGetTab(viewer, &tabs));
    2742:   PetscCall(PetscViewerASCIISetTab(viewer, ((PetscObject)snes)->tablevel));
    2743:   PetscCall(PetscViewerASCIIPrintf(viewer, "  ---------- Testing Jacobian -------------\n"));
    2744:   if (!complete_print && !directionsprinted) {
    2745:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Run with -snes_test_jacobian_view and optionally -snes_test_jacobian <threshold> to show difference\n"));
    2746:     PetscCall(PetscViewerASCIIPrintf(viewer, "    of hand-coded and finite difference Jacobian entries greater than <threshold>.\n"));
    2747:   }
    2748:   if (!directionsprinted) {
    2749:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Testing hand-coded Jacobian, if (for double precision runs) ||J - Jfd||_F/||J||_F is\n"));
    2750:     PetscCall(PetscViewerASCIIPrintf(viewer, "    O(1.e-8), the hand-coded Jacobian is probably correct.\n"));
    2751:     directionsprinted = PETSC_TRUE;
    2752:   }
    2753:   if (complete_print) PetscCall(PetscViewerPushFormat(mviewer, format));

    2755:   PetscCall(PetscObjectTypeCompare((PetscObject)snes->jacobian, MATMFFD, &flg));
    2756:   if (!flg) jacobian = snes->jacobian;
    2757:   else jacobian = snes->jacobian_pre;

    2759:   if (!x) PetscCall(MatCreateVecs(jacobian, &x, NULL));
    2760:   else PetscCall(PetscObjectReference((PetscObject)x));
    2761:   PetscCall(VecDuplicate(x, &f));

    2763:   /* evaluate the function at this point because SNESComputeJacobianDefault() assumes that the function has been evaluated and put into snes->vec_func */
    2764:   PetscCall(SNESComputeFunction(snes, x, f));
    2765:   PetscCall(VecDestroy(&f));
    2766:   PetscCall(PetscObjectTypeCompare((PetscObject)snes, SNESKSPTRANSPOSEONLY, &istranspose));
    2767:   while (jacobian) {
    2768:     Mat JT = NULL, Jsave = NULL;

    2770:     if (istranspose) {
    2771:       PetscCall(MatCreateTranspose(jacobian, &JT));
    2772:       Jsave    = jacobian;
    2773:       jacobian = JT;
    2774:     }
    2775:     PetscCall(PetscObjectBaseTypeCompareAny((PetscObject)jacobian, &flg, MATSEQAIJ, MATMPIAIJ, MATSEQDENSE, MATMPIDENSE, MATSEQBAIJ, MATMPIBAIJ, MATSEQSBAIJ, MATMPISBAIJ, ""));
    2776:     if (flg) {
    2777:       A = jacobian;
    2778:       PetscCall(PetscObjectReference((PetscObject)A));
    2779:     } else {
    2780:       PetscCall(MatComputeOperator(jacobian, MATAIJ, &A));
    2781:     }

    2783:     PetscCall(MatGetType(A, &mattype));
    2784:     PetscCall(MatGetSize(A, &M, &N));
    2785:     PetscCall(MatGetLocalSize(A, &m, &n));
    2786:     PetscCall(MatCreate(PetscObjectComm((PetscObject)A), &B));
    2787:     PetscCall(MatSetType(B, mattype));
    2788:     PetscCall(MatSetSizes(B, m, n, M, N));
    2789:     PetscCall(MatSetBlockSizesFromMats(B, A, A));
    2790:     PetscCall(MatSetUp(B));
    2791:     PetscCall(MatSetOption(B, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_FALSE));

    2793:     PetscCall(SNESGetFunction(snes, NULL, NULL, &functx));
    2794:     PetscCall(SNESComputeJacobianDefault(snes, x, B, B, functx));

    2796:     PetscCall(MatDuplicate(B, MAT_COPY_VALUES, &D));
    2797:     PetscCall(MatAYPX(D, -1.0, A, DIFFERENT_NONZERO_PATTERN));
    2798:     PetscCall(MatNorm(D, NORM_FROBENIUS, &nrm));
    2799:     PetscCall(MatNorm(A, NORM_FROBENIUS, &gnorm));
    2800:     PetscCall(MatDestroy(&D));
    2801:     if (!gnorm) gnorm = 1; /* just in case */
    2802:     PetscCall(PetscViewerASCIIPrintf(viewer, "  ||J - Jfd||_F/||J||_F = %g, ||J - Jfd||_F = %g\n", (double)(nrm / gnorm), (double)nrm));

    2804:     if (complete_print) {
    2805:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded Jacobian ----------\n"));
    2806:       PetscCall(MatView(A, mviewer));
    2807:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Finite difference Jacobian ----------\n"));
    2808:       PetscCall(MatView(B, mviewer));
    2809:     }

    2811:     if (threshold_print || complete_print) {
    2812:       PetscInt           Istart, Iend, *ccols, bncols, cncols, j, row;
    2813:       PetscScalar       *cvals;
    2814:       const PetscInt    *bcols;
    2815:       const PetscScalar *bvals;

    2817:       PetscCall(MatCreate(PetscObjectComm((PetscObject)A), &C));
    2818:       PetscCall(MatSetType(C, mattype));
    2819:       PetscCall(MatSetSizes(C, m, n, M, N));
    2820:       PetscCall(MatSetBlockSizesFromMats(C, A, A));
    2821:       PetscCall(MatSetUp(C));
    2822:       PetscCall(MatSetOption(C, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_FALSE));

    2824:       PetscCall(MatAYPX(B, -1.0, A, DIFFERENT_NONZERO_PATTERN));
    2825:       PetscCall(MatGetOwnershipRange(B, &Istart, &Iend));

    2827:       for (row = Istart; row < Iend; row++) {
    2828:         PetscCall(MatGetRow(B, row, &bncols, &bcols, &bvals));
    2829:         PetscCall(PetscMalloc2(bncols, &ccols, bncols, &cvals));
    2830:         for (j = 0, cncols = 0; j < bncols; j++) {
    2831:           if (PetscAbsScalar(bvals[j]) > threshold) {
    2832:             ccols[cncols] = bcols[j];
    2833:             cvals[cncols] = bvals[j];
    2834:             cncols += 1;
    2835:           }
    2836:         }
    2837:         if (cncols) PetscCall(MatSetValues(C, 1, &row, cncols, ccols, cvals, INSERT_VALUES));
    2838:         PetscCall(MatRestoreRow(B, row, &bncols, &bcols, &bvals));
    2839:         PetscCall(PetscFree2(ccols, cvals));
    2840:       }
    2841:       PetscCall(MatAssemblyBegin(C, MAT_FINAL_ASSEMBLY));
    2842:       PetscCall(MatAssemblyEnd(C, MAT_FINAL_ASSEMBLY));
    2843:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded minus finite-difference Jacobian with tolerance %g ----------\n", (double)threshold));
    2844:       PetscCall(MatView(C, complete_print ? mviewer : viewer));
    2845:       PetscCall(MatDestroy(&C));
    2846:     }
    2847:     PetscCall(MatDestroy(&A));
    2848:     PetscCall(MatDestroy(&B));
    2849:     PetscCall(MatDestroy(&JT));
    2850:     if (Jsave) jacobian = Jsave;
    2851:     if (jacobian != snes->jacobian_pre) {
    2852:       jacobian = snes->jacobian_pre;
    2853:       PetscCall(PetscViewerASCIIPrintf(viewer, "  ---------- Testing Jacobian for preconditioner -------------\n"));
    2854:     } else jacobian = NULL;
    2855:   }
    2856:   PetscCall(VecDestroy(&x));
    2857:   if (complete_print) PetscCall(PetscViewerPopFormat(mviewer));
    2858:   if (mviewer) PetscCall(PetscViewerDestroy(&mviewer));
    2859:   PetscCall(PetscViewerASCIISetTab(viewer, tabs));
    2860:   PetscFunctionReturn(PETSC_SUCCESS);
    2861: }

    2863: /*@
    2864:   SNESComputeJacobian - Computes the Jacobian matrix that has been set with `SNESSetJacobian()`.

    2866:   Collective

    2868:   Input Parameters:
    2869: + snes - the `SNES` context
    2870: - X    - input vector

    2872:   Output Parameters:
    2873: + A - Jacobian matrix
    2874: - B - optional matrix for building the preconditioner, usually the same as `A`

    2876:   Options Database Keys:
    2877: + -snes_lag_preconditioner <lag>           - how often to rebuild preconditioner
    2878: . -snes_lag_jacobian <lag>                 - how often to rebuild Jacobian
    2879: . -snes_test_jacobian <optional threshold> - compare the user provided Jacobian with one compute via finite differences to check for errors.  If a threshold is given, display only those entries whose difference is greater than the threshold.
    2880: . -snes_test_jacobian_view                 - display the user provided Jacobian, the finite difference Jacobian and the difference between them to help users detect the location of errors in the user provided Jacobian
    2881: . -snes_compare_explicit                   - Compare the computed Jacobian to the finite difference Jacobian and output the differences
    2882: . -snes_compare_explicit_draw              - Compare the computed Jacobian to the finite difference Jacobian and draw the result
    2883: . -snes_compare_explicit_contour           - Compare the computed Jacobian to the finite difference Jacobian and draw a contour plot with the result
    2884: . -snes_compare_operator                   - Make the comparison options above use the operator instead of the preconditioning matrix
    2885: . -snes_compare_coloring                   - Compute the finite difference Jacobian using coloring and display norms of difference
    2886: . -snes_compare_coloring_display           - Compute the finite difference Jacobian using coloring and display verbose differences
    2887: . -snes_compare_coloring_threshold         - Display only those matrix entries that differ by more than a given threshold
    2888: . -snes_compare_coloring_threshold_atol    - Absolute tolerance for difference in matrix entries to be displayed by `-snes_compare_coloring_threshold`
    2889: . -snes_compare_coloring_threshold_rtol    - Relative tolerance for difference in matrix entries to be displayed by `-snes_compare_coloring_threshold`
    2890: . -snes_compare_coloring_draw              - Compute the finite difference Jacobian using coloring and draw differences
    2891: - -snes_compare_coloring_draw_contour      - Compute the finite difference Jacobian using coloring and show contours of matrices and differences

    2893:   Level: developer

    2895:   Note:
    2896:   Most users should not need to explicitly call this routine, as it
    2897:   is used internally within the nonlinear solvers.

    2899:   Developer Note:
    2900:   This has duplicative ways of checking the accuracy of the user provided Jacobian (see the options above). This is for historical reasons, the routine `SNESTestJacobian()` use to used
    2901:   with the `SNESType` of test that has been removed.

    2903: .seealso: [](ch_snes), `SNESSetJacobian()`, `KSPSetOperators()`, `MatStructure`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobian()`
    2904: @*/
    2905: PetscErrorCode SNESComputeJacobian(SNES snes, Vec X, Mat A, Mat B)
    2906: {
    2907:   PetscBool flag;
    2908:   DM        dm;
    2909:   DMSNES    sdm;
    2910:   KSP       ksp;

    2912:   PetscFunctionBegin;
    2915:   PetscCheckSameComm(snes, 1, X, 2);
    2916:   PetscCall(VecValidValues_Internal(X, 2, PETSC_TRUE));
    2917:   PetscCall(SNESGetDM(snes, &dm));
    2918:   PetscCall(DMGetDMSNES(dm, &sdm));

    2920:   /* make sure that MatAssemblyBegin/End() is called on A matrix if it is matrix-free */
    2921:   if (snes->lagjacobian == -2) {
    2922:     snes->lagjacobian = -1;

    2924:     PetscCall(PetscInfo(snes, "Recomputing Jacobian/preconditioner because lag is -2 (means compute Jacobian, but then never again) \n"));
    2925:   } else if (snes->lagjacobian == -1) {
    2926:     PetscCall(PetscInfo(snes, "Reusing Jacobian/preconditioner because lag is -1\n"));
    2927:     PetscCall(PetscObjectTypeCompare((PetscObject)A, MATMFFD, &flag));
    2928:     if (flag) {
    2929:       PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    2930:       PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
    2931:     }
    2932:     PetscFunctionReturn(PETSC_SUCCESS);
    2933:   } else if (snes->lagjacobian > 1 && (snes->iter + snes->jac_iter) % snes->lagjacobian) {
    2934:     PetscCall(PetscInfo(snes, "Reusing Jacobian/preconditioner because lag is %" PetscInt_FMT " and SNES iteration is %" PetscInt_FMT "\n", snes->lagjacobian, snes->iter));
    2935:     PetscCall(PetscObjectTypeCompare((PetscObject)A, MATMFFD, &flag));
    2936:     if (flag) {
    2937:       PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    2938:       PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
    2939:     }
    2940:     PetscFunctionReturn(PETSC_SUCCESS);
    2941:   }
    2942:   if (snes->npc && snes->npcside == PC_LEFT) {
    2943:     PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    2944:     PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
    2945:     PetscFunctionReturn(PETSC_SUCCESS);
    2946:   }

    2948:   PetscCall(PetscLogEventBegin(SNES_JacobianEval, snes, X, A, B));
    2949:   PetscCall(VecLockReadPush(X));
    2950:   {
    2951:     void           *ctx;
    2952:     SNESJacobianFn *J;
    2953:     PetscCall(DMSNESGetJacobian(dm, &J, &ctx));
    2954:     PetscCallBack("SNES callback Jacobian", (*J)(snes, X, A, B, ctx));
    2955:   }
    2956:   PetscCall(VecLockReadPop(X));
    2957:   PetscCall(PetscLogEventEnd(SNES_JacobianEval, snes, X, A, B));

    2959:   /* attach latest linearization point to the preconditioning matrix */
    2960:   PetscCall(PetscObjectCompose((PetscObject)B, "__SNES_latest_X", (PetscObject)X));

    2962:   /* the next line ensures that snes->ksp exists */
    2963:   PetscCall(SNESGetKSP(snes, &ksp));
    2964:   if (snes->lagpreconditioner == -2) {
    2965:     PetscCall(PetscInfo(snes, "Rebuilding preconditioner exactly once since lag is -2\n"));
    2966:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_FALSE));
    2967:     snes->lagpreconditioner = -1;
    2968:   } else if (snes->lagpreconditioner == -1) {
    2969:     PetscCall(PetscInfo(snes, "Reusing preconditioner because lag is -1\n"));
    2970:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_TRUE));
    2971:   } else if (snes->lagpreconditioner > 1 && (snes->iter + snes->pre_iter) % snes->lagpreconditioner) {
    2972:     PetscCall(PetscInfo(snes, "Reusing preconditioner because lag is %" PetscInt_FMT " and SNES iteration is %" PetscInt_FMT "\n", snes->lagpreconditioner, snes->iter));
    2973:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_TRUE));
    2974:   } else {
    2975:     PetscCall(PetscInfo(snes, "Rebuilding preconditioner\n"));
    2976:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_FALSE));
    2977:   }

    2979:   /* monkey business to allow testing Jacobians in multilevel solvers.
    2980:      This is needed because the SNESTestXXX interface does not accept vectors and matrices */
    2981:   {
    2982:     Vec xsave            = snes->vec_sol;
    2983:     Mat jacobiansave     = snes->jacobian;
    2984:     Mat jacobian_presave = snes->jacobian_pre;

    2986:     snes->vec_sol      = X;
    2987:     snes->jacobian     = A;
    2988:     snes->jacobian_pre = B;
    2989:     PetscCall(SNESTestFunction(snes));
    2990:     PetscCall(SNESTestJacobian(snes));

    2992:     snes->vec_sol      = xsave;
    2993:     snes->jacobian     = jacobiansave;
    2994:     snes->jacobian_pre = jacobian_presave;
    2995:   }

    2997:   {
    2998:     PetscBool flag = PETSC_FALSE, flag_draw = PETSC_FALSE, flag_contour = PETSC_FALSE, flag_operator = PETSC_FALSE;
    2999:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_explicit", NULL, NULL, &flag));
    3000:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_explicit_draw", NULL, NULL, &flag_draw));
    3001:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_explicit_draw_contour", NULL, NULL, &flag_contour));
    3002:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_operator", NULL, NULL, &flag_operator));
    3003:     if (flag || flag_draw || flag_contour) {
    3004:       Mat         Bexp_mine = NULL, Bexp, FDexp;
    3005:       PetscViewer vdraw, vstdout;
    3006:       PetscBool   flg;
    3007:       if (flag_operator) {
    3008:         PetscCall(MatComputeOperator(A, MATAIJ, &Bexp_mine));
    3009:         Bexp = Bexp_mine;
    3010:       } else {
    3011:         /* See if the preconditioning matrix can be viewed and added directly */
    3012:         PetscCall(PetscObjectBaseTypeCompareAny((PetscObject)B, &flg, MATSEQAIJ, MATMPIAIJ, MATSEQDENSE, MATMPIDENSE, MATSEQBAIJ, MATMPIBAIJ, MATSEQSBAIJ, MATMPIBAIJ, ""));
    3013:         if (flg) Bexp = B;
    3014:         else {
    3015:           /* If the "preconditioning" matrix is itself MATSHELL or some other type without direct support */
    3016:           PetscCall(MatComputeOperator(B, MATAIJ, &Bexp_mine));
    3017:           Bexp = Bexp_mine;
    3018:         }
    3019:       }
    3020:       PetscCall(MatConvert(Bexp, MATSAME, MAT_INITIAL_MATRIX, &FDexp));
    3021:       PetscCall(SNESComputeJacobianDefault(snes, X, FDexp, FDexp, NULL));
    3022:       PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)snes), &vstdout));
    3023:       if (flag_draw || flag_contour) {
    3024:         PetscCall(PetscViewerDrawOpen(PetscObjectComm((PetscObject)snes), NULL, "Explicit Jacobians", PETSC_DECIDE, PETSC_DECIDE, 300, 300, &vdraw));
    3025:         if (flag_contour) PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3026:       } else vdraw = NULL;
    3027:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Explicit %s\n", flag_operator ? "Jacobian" : "preconditioning Jacobian"));
    3028:       if (flag) PetscCall(MatView(Bexp, vstdout));
    3029:       if (vdraw) PetscCall(MatView(Bexp, vdraw));
    3030:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Finite difference Jacobian\n"));
    3031:       if (flag) PetscCall(MatView(FDexp, vstdout));
    3032:       if (vdraw) PetscCall(MatView(FDexp, vdraw));
    3033:       PetscCall(MatAYPX(FDexp, -1.0, Bexp, SAME_NONZERO_PATTERN));
    3034:       PetscCall(PetscViewerASCIIPrintf(vstdout, "User-provided matrix minus finite difference Jacobian\n"));
    3035:       if (flag) PetscCall(MatView(FDexp, vstdout));
    3036:       if (vdraw) { /* Always use contour for the difference */
    3037:         PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3038:         PetscCall(MatView(FDexp, vdraw));
    3039:         PetscCall(PetscViewerPopFormat(vdraw));
    3040:       }
    3041:       if (flag_contour) PetscCall(PetscViewerPopFormat(vdraw));
    3042:       PetscCall(PetscViewerDestroy(&vdraw));
    3043:       PetscCall(MatDestroy(&Bexp_mine));
    3044:       PetscCall(MatDestroy(&FDexp));
    3045:     }
    3046:   }
    3047:   {
    3048:     PetscBool flag = PETSC_FALSE, flag_display = PETSC_FALSE, flag_draw = PETSC_FALSE, flag_contour = PETSC_FALSE, flag_threshold = PETSC_FALSE;
    3049:     PetscReal threshold_atol = PETSC_SQRT_MACHINE_EPSILON, threshold_rtol = 10 * PETSC_SQRT_MACHINE_EPSILON;
    3050:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring", NULL, NULL, &flag));
    3051:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_display", NULL, NULL, &flag_display));
    3052:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_draw", NULL, NULL, &flag_draw));
    3053:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_draw_contour", NULL, NULL, &flag_contour));
    3054:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_threshold", NULL, NULL, &flag_threshold));
    3055:     if (flag_threshold) {
    3056:       PetscCall(PetscOptionsGetReal(((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_threshold_rtol", &threshold_rtol, NULL));
    3057:       PetscCall(PetscOptionsGetReal(((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_threshold_atol", &threshold_atol, NULL));
    3058:     }
    3059:     if (flag || flag_display || flag_draw || flag_contour || flag_threshold) {
    3060:       Mat             Bfd;
    3061:       PetscViewer     vdraw, vstdout;
    3062:       MatColoring     coloring;
    3063:       ISColoring      iscoloring;
    3064:       MatFDColoring   matfdcoloring;
    3065:       SNESFunctionFn *func;
    3066:       void           *funcctx;
    3067:       PetscReal       norm1, norm2, normmax;

    3069:       PetscCall(MatDuplicate(B, MAT_DO_NOT_COPY_VALUES, &Bfd));
    3070:       PetscCall(MatColoringCreate(Bfd, &coloring));
    3071:       PetscCall(MatColoringSetType(coloring, MATCOLORINGSL));
    3072:       PetscCall(MatColoringSetFromOptions(coloring));
    3073:       PetscCall(MatColoringApply(coloring, &iscoloring));
    3074:       PetscCall(MatColoringDestroy(&coloring));
    3075:       PetscCall(MatFDColoringCreate(Bfd, iscoloring, &matfdcoloring));
    3076:       PetscCall(MatFDColoringSetFromOptions(matfdcoloring));
    3077:       PetscCall(MatFDColoringSetUp(Bfd, iscoloring, matfdcoloring));
    3078:       PetscCall(ISColoringDestroy(&iscoloring));

    3080:       /* This method of getting the function is currently unreliable since it doesn't work for DM local functions. */
    3081:       PetscCall(SNESGetFunction(snes, NULL, &func, &funcctx));
    3082:       PetscCall(MatFDColoringSetFunction(matfdcoloring, (PetscErrorCode (*)(void))func, funcctx));
    3083:       PetscCall(PetscObjectSetOptionsPrefix((PetscObject)matfdcoloring, ((PetscObject)snes)->prefix));
    3084:       PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)matfdcoloring, "coloring_"));
    3085:       PetscCall(MatFDColoringSetFromOptions(matfdcoloring));
    3086:       PetscCall(MatFDColoringApply(Bfd, matfdcoloring, X, snes));
    3087:       PetscCall(MatFDColoringDestroy(&matfdcoloring));

    3089:       PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)snes), &vstdout));
    3090:       if (flag_draw || flag_contour) {
    3091:         PetscCall(PetscViewerDrawOpen(PetscObjectComm((PetscObject)snes), NULL, "Colored Jacobians", PETSC_DECIDE, PETSC_DECIDE, 300, 300, &vdraw));
    3092:         if (flag_contour) PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3093:       } else vdraw = NULL;
    3094:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Explicit preconditioning Jacobian\n"));
    3095:       if (flag_display) PetscCall(MatView(B, vstdout));
    3096:       if (vdraw) PetscCall(MatView(B, vdraw));
    3097:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Colored Finite difference Jacobian\n"));
    3098:       if (flag_display) PetscCall(MatView(Bfd, vstdout));
    3099:       if (vdraw) PetscCall(MatView(Bfd, vdraw));
    3100:       PetscCall(MatAYPX(Bfd, -1.0, B, SAME_NONZERO_PATTERN));
    3101:       PetscCall(MatNorm(Bfd, NORM_1, &norm1));
    3102:       PetscCall(MatNorm(Bfd, NORM_FROBENIUS, &norm2));
    3103:       PetscCall(MatNorm(Bfd, NORM_MAX, &normmax));
    3104:       PetscCall(PetscViewerASCIIPrintf(vstdout, "User-provided matrix minus finite difference Jacobian, norm1=%g normFrob=%g normmax=%g\n", (double)norm1, (double)norm2, (double)normmax));
    3105:       if (flag_display) PetscCall(MatView(Bfd, vstdout));
    3106:       if (vdraw) { /* Always use contour for the difference */
    3107:         PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3108:         PetscCall(MatView(Bfd, vdraw));
    3109:         PetscCall(PetscViewerPopFormat(vdraw));
    3110:       }
    3111:       if (flag_contour) PetscCall(PetscViewerPopFormat(vdraw));

    3113:       if (flag_threshold) {
    3114:         PetscInt bs, rstart, rend, i;
    3115:         PetscCall(MatGetBlockSize(B, &bs));
    3116:         PetscCall(MatGetOwnershipRange(B, &rstart, &rend));
    3117:         for (i = rstart; i < rend; i++) {
    3118:           const PetscScalar *ba, *ca;
    3119:           const PetscInt    *bj, *cj;
    3120:           PetscInt           bn, cn, j, maxentrycol = -1, maxdiffcol = -1, maxrdiffcol = -1;
    3121:           PetscReal          maxentry = 0, maxdiff = 0, maxrdiff = 0;
    3122:           PetscCall(MatGetRow(B, i, &bn, &bj, &ba));
    3123:           PetscCall(MatGetRow(Bfd, i, &cn, &cj, &ca));
    3124:           PetscCheck(bn == cn, ((PetscObject)A)->comm, PETSC_ERR_PLIB, "Unexpected different nonzero pattern in -snes_compare_coloring_threshold");
    3125:           for (j = 0; j < bn; j++) {
    3126:             PetscReal rdiff = PetscAbsScalar(ca[j]) / (threshold_atol + threshold_rtol * PetscAbsScalar(ba[j]));
    3127:             if (PetscAbsScalar(ba[j]) > PetscAbs(maxentry)) {
    3128:               maxentrycol = bj[j];
    3129:               maxentry    = PetscRealPart(ba[j]);
    3130:             }
    3131:             if (PetscAbsScalar(ca[j]) > PetscAbs(maxdiff)) {
    3132:               maxdiffcol = bj[j];
    3133:               maxdiff    = PetscRealPart(ca[j]);
    3134:             }
    3135:             if (rdiff > maxrdiff) {
    3136:               maxrdiffcol = bj[j];
    3137:               maxrdiff    = rdiff;
    3138:             }
    3139:           }
    3140:           if (maxrdiff > 1) {
    3141:             PetscCall(PetscViewerASCIIPrintf(vstdout, "row %" PetscInt_FMT " (maxentry=%g at %" PetscInt_FMT ", maxdiff=%g at %" PetscInt_FMT ", maxrdiff=%g at %" PetscInt_FMT "):", i, (double)maxentry, maxentrycol, (double)maxdiff, maxdiffcol, (double)maxrdiff, maxrdiffcol));
    3142:             for (j = 0; j < bn; j++) {
    3143:               PetscReal rdiff;
    3144:               rdiff = PetscAbsScalar(ca[j]) / (threshold_atol + threshold_rtol * PetscAbsScalar(ba[j]));
    3145:               if (rdiff > 1) PetscCall(PetscViewerASCIIPrintf(vstdout, " (%" PetscInt_FMT ",%g:%g)", bj[j], (double)PetscRealPart(ba[j]), (double)PetscRealPart(ca[j])));
    3146:             }
    3147:             PetscCall(PetscViewerASCIIPrintf(vstdout, "\n"));
    3148:           }
    3149:           PetscCall(MatRestoreRow(B, i, &bn, &bj, &ba));
    3150:           PetscCall(MatRestoreRow(Bfd, i, &cn, &cj, &ca));
    3151:         }
    3152:       }
    3153:       PetscCall(PetscViewerDestroy(&vdraw));
    3154:       PetscCall(MatDestroy(&Bfd));
    3155:     }
    3156:   }
    3157:   PetscFunctionReturn(PETSC_SUCCESS);
    3158: }

    3160: /*@C
    3161:   SNESSetJacobian - Sets the function to compute Jacobian as well as the
    3162:   location to store the matrix.

    3164:   Logically Collective

    3166:   Input Parameters:
    3167: + snes - the `SNES` context
    3168: . Amat - the matrix that defines the (approximate) Jacobian
    3169: . Pmat - the matrix to be used in constructing the preconditioner, usually the same as `Amat`.
    3170: . J    - Jacobian evaluation routine (if `NULL` then `SNES` retains any previously set value), see `SNESJacobianFn` for details
    3171: - ctx  - [optional] user-defined context for private data for the
    3172:          Jacobian evaluation routine (may be `NULL`) (if `NULL` then `SNES` retains any previously set value)

    3174:   Level: beginner

    3176:   Notes:
    3177:   If the `Amat` matrix and `Pmat` matrix are different you must call `MatAssemblyBegin()`/`MatAssemblyEnd()` on
    3178:   each matrix.

    3180:   If you know the operator `Amat` has a null space you can use `MatSetNullSpace()` and `MatSetTransposeNullSpace()` to supply the null
    3181:   space to `Amat` and the `KSP` solvers will automatically use that null space as needed during the solution process.

    3183:   If using `SNESComputeJacobianDefaultColor()` to assemble a Jacobian, the `ctx` argument
    3184:   must be a `MatFDColoring`.

    3186:   Other defect-correction schemes can be used by computing a different matrix in place of the Jacobian.  One common
    3187:   example is to use the "Picard linearization" which only differentiates through the highest order parts of each term using `SNESSetPicard()`

    3189: .seealso: [](ch_snes), `SNES`, `KSPSetOperators()`, `SNESSetFunction()`, `MatMFFDComputeJacobian()`, `SNESComputeJacobianDefaultColor()`, `MatStructure`,
    3190:           `SNESSetPicard()`, `SNESJacobianFn`, `SNESFunctionFn`
    3191: @*/
    3192: PetscErrorCode SNESSetJacobian(SNES snes, Mat Amat, Mat Pmat, SNESJacobianFn *J, void *ctx)
    3193: {
    3194:   DM dm;

    3196:   PetscFunctionBegin;
    3200:   if (Amat) PetscCheckSameComm(snes, 1, Amat, 2);
    3201:   if (Pmat) PetscCheckSameComm(snes, 1, Pmat, 3);
    3202:   PetscCall(SNESGetDM(snes, &dm));
    3203:   PetscCall(DMSNESSetJacobian(dm, J, ctx));
    3204:   if (Amat) {
    3205:     PetscCall(PetscObjectReference((PetscObject)Amat));
    3206:     PetscCall(MatDestroy(&snes->jacobian));

    3208:     snes->jacobian = Amat;
    3209:   }
    3210:   if (Pmat) {
    3211:     PetscCall(PetscObjectReference((PetscObject)Pmat));
    3212:     PetscCall(MatDestroy(&snes->jacobian_pre));

    3214:     snes->jacobian_pre = Pmat;
    3215:   }
    3216:   PetscFunctionReturn(PETSC_SUCCESS);
    3217: }

    3219: /*@C
    3220:   SNESGetJacobian - Returns the Jacobian matrix and optionally the user
    3221:   provided context for evaluating the Jacobian.

    3223:   Not Collective, but `Mat` object will be parallel if `SNES` is

    3225:   Input Parameter:
    3226: . snes - the nonlinear solver context

    3228:   Output Parameters:
    3229: + Amat - location to stash (approximate) Jacobian matrix (or `NULL`)
    3230: . Pmat - location to stash matrix used to compute the preconditioner (or `NULL`)
    3231: . J    - location to put Jacobian function (or `NULL`), for calling sequence see `SNESJacobianFn`
    3232: - ctx  - location to stash Jacobian ctx (or `NULL`)

    3234:   Level: advanced

    3236: .seealso: [](ch_snes), `SNES`, `Mat`, `SNESSetJacobian()`, `SNESComputeJacobian()`, `SNESJacobianFn`, `SNESGetFunction()`
    3237: @*/
    3238: PetscErrorCode SNESGetJacobian(SNES snes, Mat *Amat, Mat *Pmat, SNESJacobianFn **J, void **ctx)
    3239: {
    3240:   DM dm;

    3242:   PetscFunctionBegin;
    3244:   if (Amat) *Amat = snes->jacobian;
    3245:   if (Pmat) *Pmat = snes->jacobian_pre;
    3246:   PetscCall(SNESGetDM(snes, &dm));
    3247:   PetscCall(DMSNESGetJacobian(dm, J, ctx));
    3248:   PetscFunctionReturn(PETSC_SUCCESS);
    3249: }

    3251: static PetscErrorCode SNESSetDefaultComputeJacobian(SNES snes)
    3252: {
    3253:   DM     dm;
    3254:   DMSNES sdm;

    3256:   PetscFunctionBegin;
    3257:   PetscCall(SNESGetDM(snes, &dm));
    3258:   PetscCall(DMGetDMSNES(dm, &sdm));
    3259:   if (!sdm->ops->computejacobian && snes->jacobian_pre) {
    3260:     DM        dm;
    3261:     PetscBool isdense, ismf;

    3263:     PetscCall(SNESGetDM(snes, &dm));
    3264:     PetscCall(PetscObjectTypeCompareAny((PetscObject)snes->jacobian_pre, &isdense, MATSEQDENSE, MATMPIDENSE, MATDENSE, NULL));
    3265:     PetscCall(PetscObjectTypeCompareAny((PetscObject)snes->jacobian_pre, &ismf, MATMFFD, MATSHELL, NULL));
    3266:     if (isdense) {
    3267:       PetscCall(DMSNESSetJacobian(dm, SNESComputeJacobianDefault, NULL));
    3268:     } else if (!ismf) {
    3269:       PetscCall(DMSNESSetJacobian(dm, SNESComputeJacobianDefaultColor, NULL));
    3270:     }
    3271:   }
    3272:   PetscFunctionReturn(PETSC_SUCCESS);
    3273: }

    3275: /*@
    3276:   SNESSetUp - Sets up the internal data structures for the later use
    3277:   of a nonlinear solver `SNESSolve()`.

    3279:   Collective

    3281:   Input Parameter:
    3282: . snes - the `SNES` context

    3284:   Level: advanced

    3286:   Note:
    3287:   For basic use of the `SNES` solvers the user does not need to explicitly call
    3288:   `SNESSetUp()`, since these actions will automatically occur during
    3289:   the call to `SNESSolve()`.  However, if one wishes to control this
    3290:   phase separately, `SNESSetUp()` should be called after `SNESCreate()`
    3291:   and optional routines of the form SNESSetXXX(), but before `SNESSolve()`.

    3293: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESSolve()`, `SNESDestroy()`, `SNESSetFromOptions()`
    3294: @*/
    3295: PetscErrorCode SNESSetUp(SNES snes)
    3296: {
    3297:   DM             dm;
    3298:   DMSNES         sdm;
    3299:   SNESLineSearch linesearch, pclinesearch;
    3300:   void          *lsprectx, *lspostctx;
    3301:   PetscBool      mf_operator, mf;
    3302:   Vec            f, fpc;
    3303:   void          *funcctx;
    3304:   void          *jacctx, *appctx;
    3305:   Mat            j, jpre;
    3306:   PetscErrorCode (*precheck)(SNESLineSearch, Vec, Vec, PetscBool *, void *);
    3307:   PetscErrorCode (*postcheck)(SNESLineSearch, Vec, Vec, Vec, PetscBool *, PetscBool *, void *);
    3308:   SNESFunctionFn *func;
    3309:   SNESJacobianFn *jac;

    3311:   PetscFunctionBegin;
    3313:   if (snes->setupcalled) PetscFunctionReturn(PETSC_SUCCESS);
    3314:   PetscCall(PetscLogEventBegin(SNES_SetUp, snes, 0, 0, 0));

    3316:   if (!((PetscObject)snes)->type_name) PetscCall(SNESSetType(snes, SNESNEWTONLS));

    3318:   PetscCall(SNESGetFunction(snes, &snes->vec_func, NULL, NULL));

    3320:   PetscCall(SNESGetDM(snes, &dm));
    3321:   PetscCall(DMGetDMSNES(dm, &sdm));
    3322:   PetscCall(SNESSetDefaultComputeJacobian(snes));

    3324:   if (!snes->vec_func) PetscCall(DMCreateGlobalVector(dm, &snes->vec_func));

    3326:   if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));

    3328:   if (snes->linesearch) {
    3329:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    3330:     PetscCall(SNESLineSearchSetFunction(snes->linesearch, SNESComputeFunction));
    3331:   }

    3333:   PetscCall(SNESGetUseMatrixFree(snes, &mf_operator, &mf));
    3334:   if (snes->npc && snes->npcside == PC_LEFT) {
    3335:     snes->mf          = PETSC_TRUE;
    3336:     snes->mf_operator = PETSC_FALSE;
    3337:   }

    3339:   if (snes->npc) {
    3340:     /* copy the DM over */
    3341:     PetscCall(SNESGetDM(snes, &dm));
    3342:     PetscCall(SNESSetDM(snes->npc, dm));

    3344:     PetscCall(SNESGetFunction(snes, &f, &func, &funcctx));
    3345:     PetscCall(VecDuplicate(f, &fpc));
    3346:     PetscCall(SNESSetFunction(snes->npc, fpc, func, funcctx));
    3347:     PetscCall(SNESGetJacobian(snes, &j, &jpre, &jac, &jacctx));
    3348:     PetscCall(SNESSetJacobian(snes->npc, j, jpre, jac, jacctx));
    3349:     PetscCall(SNESGetApplicationContext(snes, &appctx));
    3350:     PetscCall(SNESSetApplicationContext(snes->npc, appctx));
    3351:     PetscCall(SNESSetUseMatrixFree(snes->npc, mf_operator, mf));
    3352:     PetscCall(VecDestroy(&fpc));

    3354:     /* copy the function pointers over */
    3355:     PetscCall(PetscObjectCopyFortranFunctionPointers((PetscObject)snes, (PetscObject)snes->npc));

    3357:     /* default to 1 iteration */
    3358:     PetscCall(SNESSetTolerances(snes->npc, 0.0, 0.0, 0.0, 1, snes->npc->max_funcs));
    3359:     if (snes->npcside == PC_RIGHT) {
    3360:       PetscCall(SNESSetNormSchedule(snes->npc, SNES_NORM_FINAL_ONLY));
    3361:     } else {
    3362:       PetscCall(SNESSetNormSchedule(snes->npc, SNES_NORM_NONE));
    3363:     }
    3364:     PetscCall(SNESSetFromOptions(snes->npc));

    3366:     /* copy the line search context over */
    3367:     if (snes->linesearch && snes->npc->linesearch) {
    3368:       PetscCall(SNESGetLineSearch(snes, &linesearch));
    3369:       PetscCall(SNESGetLineSearch(snes->npc, &pclinesearch));
    3370:       PetscCall(SNESLineSearchGetPreCheck(linesearch, &precheck, &lsprectx));
    3371:       PetscCall(SNESLineSearchGetPostCheck(linesearch, &postcheck, &lspostctx));
    3372:       PetscCall(SNESLineSearchSetPreCheck(pclinesearch, precheck, lsprectx));
    3373:       PetscCall(SNESLineSearchSetPostCheck(pclinesearch, postcheck, lspostctx));
    3374:       PetscCall(PetscObjectCopyFortranFunctionPointers((PetscObject)linesearch, (PetscObject)pclinesearch));
    3375:     }
    3376:   }
    3377:   if (snes->mf) PetscCall(SNESSetUpMatrixFree_Private(snes, snes->mf_operator, snes->mf_version));
    3378:   if (snes->ops->usercompute && !snes->ctx) PetscCallBack("SNES callback compute application context", (*snes->ops->usercompute)(snes, &snes->ctx));

    3380:   snes->jac_iter = 0;
    3381:   snes->pre_iter = 0;

    3383:   PetscTryTypeMethod(snes, setup);

    3385:   PetscCall(SNESSetDefaultComputeJacobian(snes));

    3387:   if (snes->npc && snes->npcside == PC_LEFT) {
    3388:     if (snes->functype == SNES_FUNCTION_PRECONDITIONED) {
    3389:       if (snes->linesearch) {
    3390:         PetscCall(SNESGetLineSearch(snes, &linesearch));
    3391:         PetscCall(SNESLineSearchSetFunction(linesearch, SNESComputeFunctionDefaultNPC));
    3392:       }
    3393:     }
    3394:   }
    3395:   PetscCall(PetscLogEventEnd(SNES_SetUp, snes, 0, 0, 0));
    3396:   snes->setupcalled = PETSC_TRUE;
    3397:   PetscFunctionReturn(PETSC_SUCCESS);
    3398: }

    3400: /*@
    3401:   SNESReset - Resets a `SNES` context to the state it was in before `SNESSetUp()` was called and removes any allocated `Vec` and `Mat` from its data structures

    3403:   Collective

    3405:   Input Parameter:
    3406: . snes - the nonlinear iterative solver context obtained from `SNESCreate()`

    3408:   Level: intermediate

    3410:   Notes:
    3411:   Any options set on the `SNES` object, including those set with `SNESSetFromOptions()` remain.

    3413:   Call this if you wish to reuse a `SNES` but with different size vectors

    3415:   Also calls the application context destroy routine set with `SNESSetComputeApplicationContext()`

    3417: .seealso: [](ch_snes), `SNES`, `SNESDestroy()`, `SNESCreate()`, `SNESSetUp()`, `SNESSolve()`
    3418: @*/
    3419: PetscErrorCode SNESReset(SNES snes)
    3420: {
    3421:   PetscFunctionBegin;
    3423:   if (snes->ops->ctxdestroy && snes->ctx) {
    3424:     PetscCallBack("SNES callback destroy application context", (*snes->ops->ctxdestroy)(&snes->ctx));
    3425:     snes->ctx = NULL;
    3426:   }
    3427:   if (snes->npc) PetscCall(SNESReset(snes->npc));

    3429:   PetscTryTypeMethod(snes, reset);
    3430:   if (snes->ksp) PetscCall(KSPReset(snes->ksp));

    3432:   if (snes->linesearch) PetscCall(SNESLineSearchReset(snes->linesearch));

    3434:   PetscCall(VecDestroy(&snes->vec_rhs));
    3435:   PetscCall(VecDestroy(&snes->vec_sol));
    3436:   PetscCall(VecDestroy(&snes->vec_sol_update));
    3437:   PetscCall(VecDestroy(&snes->vec_func));
    3438:   PetscCall(MatDestroy(&snes->jacobian));
    3439:   PetscCall(MatDestroy(&snes->jacobian_pre));
    3440:   PetscCall(MatDestroy(&snes->picard));
    3441:   PetscCall(VecDestroyVecs(snes->nwork, &snes->work));
    3442:   PetscCall(VecDestroyVecs(snes->nvwork, &snes->vwork));

    3444:   snes->alwayscomputesfinalresidual = PETSC_FALSE;

    3446:   snes->nwork = snes->nvwork = 0;
    3447:   snes->setupcalled          = PETSC_FALSE;
    3448:   PetscFunctionReturn(PETSC_SUCCESS);
    3449: }

    3451: /*@
    3452:   SNESConvergedReasonViewCancel - Clears all the reason view functions for a `SNES` object provided with `SNESConvergedReasonViewSet()` also
    3453:   removes the default viewer.

    3455:   Collective

    3457:   Input Parameter:
    3458: . snes - the nonlinear iterative solver context obtained from `SNESCreate()`

    3460:   Level: intermediate

    3462: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESDestroy()`, `SNESReset()`, `SNESConvergedReasonViewSet()`
    3463: @*/
    3464: PetscErrorCode SNESConvergedReasonViewCancel(SNES snes)
    3465: {
    3466:   PetscInt i;

    3468:   PetscFunctionBegin;
    3470:   for (i = 0; i < snes->numberreasonviews; i++) {
    3471:     if (snes->reasonviewdestroy[i]) PetscCall((*snes->reasonviewdestroy[i])(&snes->reasonviewcontext[i]));
    3472:   }
    3473:   snes->numberreasonviews = 0;
    3474:   PetscCall(PetscViewerDestroy(&snes->convergedreasonviewer));
    3475:   PetscFunctionReturn(PETSC_SUCCESS);
    3476: }

    3478: /*@
    3479:   SNESDestroy - Destroys the nonlinear solver context that was created
    3480:   with `SNESCreate()`.

    3482:   Collective

    3484:   Input Parameter:
    3485: . snes - the `SNES` context

    3487:   Level: beginner

    3489: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESSolve()`
    3490: @*/
    3491: PetscErrorCode SNESDestroy(SNES *snes)
    3492: {
    3493:   PetscFunctionBegin;
    3494:   if (!*snes) PetscFunctionReturn(PETSC_SUCCESS);
    3496:   if (--((PetscObject)*snes)->refct > 0) {
    3497:     *snes = NULL;
    3498:     PetscFunctionReturn(PETSC_SUCCESS);
    3499:   }

    3501:   PetscCall(SNESReset(*snes));
    3502:   PetscCall(SNESDestroy(&(*snes)->npc));

    3504:   /* if memory was published with SAWs then destroy it */
    3505:   PetscCall(PetscObjectSAWsViewOff((PetscObject)*snes));
    3506:   PetscTryTypeMethod(*snes, destroy);

    3508:   if ((*snes)->dm) PetscCall(DMCoarsenHookRemove((*snes)->dm, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, *snes));
    3509:   PetscCall(DMDestroy(&(*snes)->dm));
    3510:   PetscCall(KSPDestroy(&(*snes)->ksp));
    3511:   PetscCall(SNESLineSearchDestroy(&(*snes)->linesearch));

    3513:   PetscCall(PetscFree((*snes)->kspconvctx));
    3514:   if ((*snes)->ops->convergeddestroy) PetscCall((*(*snes)->ops->convergeddestroy)((*snes)->cnvP));
    3515:   if ((*snes)->conv_hist_alloc) PetscCall(PetscFree2((*snes)->conv_hist, (*snes)->conv_hist_its));
    3516:   PetscCall(SNESMonitorCancel(*snes));
    3517:   PetscCall(SNESConvergedReasonViewCancel(*snes));
    3518:   PetscCall(PetscHeaderDestroy(snes));
    3519:   PetscFunctionReturn(PETSC_SUCCESS);
    3520: }

    3522: /* ----------- Routines to set solver parameters ---------- */

    3524: /*@
    3525:   SNESSetLagPreconditioner - Sets when the preconditioner is rebuilt in the nonlinear solve `SNESSolve()`.

    3527:   Logically Collective

    3529:   Input Parameters:
    3530: + snes - the `SNES` context
    3531: - lag  - 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3532:          the Jacobian is built etc. -2 indicates rebuild preconditioner at next chance but then never rebuild after that

    3534:   Options Database Keys:
    3535: + -snes_lag_jacobian_persists <true,false>       - sets the persistence through multiple `SNESSolve()`
    3536: . -snes_lag_jacobian <-2,1,2,...>                - sets the lag
    3537: . -snes_lag_preconditioner_persists <true,false> - sets the persistence through multiple `SNESSolve()`
    3538: - -snes_lag_preconditioner <-2,1,2,...>          - sets the lag

    3540:   Level: intermediate

    3542:   Notes:
    3543:   The default is 1

    3545:   The preconditioner is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1 or `SNESSetLagPreconditionerPersists()` was called

    3547:   `SNESSetLagPreconditionerPersists()` allows using the same uniform lagging (for example every second linear solve) across multiple nonlinear solves.

    3549: .seealso: [](ch_snes), `SNESGetLagPreconditioner()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESSetLagPreconditionerPersists()`,
    3550:           `SNESSetLagJacobianPersists()`, `SNES`, `SNESSolve()`
    3551: @*/
    3552: PetscErrorCode SNESSetLagPreconditioner(SNES snes, PetscInt lag)
    3553: {
    3554:   PetscFunctionBegin;
    3556:   PetscCheck(lag >= -2, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag must be -2, -1, 1 or greater");
    3557:   PetscCheck(lag, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag cannot be 0");
    3559:   snes->lagpreconditioner = lag;
    3560:   PetscFunctionReturn(PETSC_SUCCESS);
    3561: }

    3563: /*@
    3564:   SNESSetGridSequence - sets the number of steps of grid sequencing that `SNES` will do

    3566:   Logically Collective

    3568:   Input Parameters:
    3569: + snes  - the `SNES` context
    3570: - steps - the number of refinements to do, defaults to 0

    3572:   Options Database Key:
    3573: . -snes_grid_sequence <steps> - Use grid sequencing to generate initial guess

    3575:   Level: intermediate

    3577:   Notes:
    3578:   Once grid sequencing is turned on `SNESSolve()` will automatically perform the solve on each grid refinement.

    3580:   Use `SNESGetSolution()` to extract the fine grid solution after grid sequencing.

    3582: .seealso: [](ch_snes), `SNES`, `SNESGetLagPreconditioner()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESGetGridSequence()`,
    3583:           `SNESSetDM()`, `SNESSolve()`
    3584: @*/
    3585: PetscErrorCode SNESSetGridSequence(SNES snes, PetscInt steps)
    3586: {
    3587:   PetscFunctionBegin;
    3590:   snes->gridsequence = steps;
    3591:   PetscFunctionReturn(PETSC_SUCCESS);
    3592: }

    3594: /*@
    3595:   SNESGetGridSequence - gets the number of steps of grid sequencing that `SNES` will do

    3597:   Logically Collective

    3599:   Input Parameter:
    3600: . snes - the `SNES` context

    3602:   Output Parameter:
    3603: . steps - the number of refinements to do, defaults to 0

    3605:   Level: intermediate

    3607: .seealso: [](ch_snes), `SNESGetLagPreconditioner()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESSetGridSequence()`
    3608: @*/
    3609: PetscErrorCode SNESGetGridSequence(SNES snes, PetscInt *steps)
    3610: {
    3611:   PetscFunctionBegin;
    3613:   *steps = snes->gridsequence;
    3614:   PetscFunctionReturn(PETSC_SUCCESS);
    3615: }

    3617: /*@
    3618:   SNESGetLagPreconditioner - Return how often the preconditioner is rebuilt

    3620:   Not Collective

    3622:   Input Parameter:
    3623: . snes - the `SNES` context

    3625:   Output Parameter:
    3626: . lag - -1 indicates NEVER rebuild, 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3627:          the Jacobian is built etc. -2 indicates rebuild preconditioner at next chance but then never rebuild after that

    3629:   Level: intermediate

    3631:   Notes:
    3632:   The default is 1

    3634:   The preconditioner is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1

    3636: .seealso: [](ch_snes), `SNES`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`
    3637: @*/
    3638: PetscErrorCode SNESGetLagPreconditioner(SNES snes, PetscInt *lag)
    3639: {
    3640:   PetscFunctionBegin;
    3642:   *lag = snes->lagpreconditioner;
    3643:   PetscFunctionReturn(PETSC_SUCCESS);
    3644: }

    3646: /*@
    3647:   SNESSetLagJacobian - Set when the Jacobian is rebuilt in the nonlinear solve. See `SNESSetLagPreconditioner()` for determining how
    3648:   often the preconditioner is rebuilt.

    3650:   Logically Collective

    3652:   Input Parameters:
    3653: + snes - the `SNES` context
    3654: - lag  - -1 indicates NEVER rebuild, 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3655:          the Jacobian is built etc. -2 means rebuild at next chance but then never again

    3657:   Options Database Keys:
    3658: + -snes_lag_jacobian_persists <true,false>       - sets the persistence through multiple SNES solves
    3659: . -snes_lag_jacobian <-2,1,2,...>                - sets the lag
    3660: . -snes_lag_preconditioner_persists <true,false> - sets the persistence through multiple SNES solves
    3661: - -snes_lag_preconditioner <-2,1,2,...>          - sets the lag.

    3663:   Level: intermediate

    3665:   Notes:
    3666:   The default is 1

    3668:   The Jacobian is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1

    3670:   If  -1 is used before the very first nonlinear solve the CODE WILL FAIL! because no Jacobian is used, use -2 to indicate you want it recomputed
    3671:   at the next Newton step but never again (unless it is reset to another value)

    3673: .seealso: [](ch_snes), `SNES`, `SNESGetLagPreconditioner()`, `SNESSetLagPreconditioner()`, `SNESGetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`
    3674: @*/
    3675: PetscErrorCode SNESSetLagJacobian(SNES snes, PetscInt lag)
    3676: {
    3677:   PetscFunctionBegin;
    3679:   PetscCheck(lag >= -2, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag must be -2, -1, 1 or greater");
    3680:   PetscCheck(lag, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag cannot be 0");
    3682:   snes->lagjacobian = lag;
    3683:   PetscFunctionReturn(PETSC_SUCCESS);
    3684: }

    3686: /*@
    3687:   SNESGetLagJacobian - Get how often the Jacobian is rebuilt. See `SNESGetLagPreconditioner()` to determine when the preconditioner is rebuilt

    3689:   Not Collective

    3691:   Input Parameter:
    3692: . snes - the `SNES` context

    3694:   Output Parameter:
    3695: . lag - -1 indicates NEVER rebuild, 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3696:          the Jacobian is built etc.

    3698:   Level: intermediate

    3700:   Notes:
    3701:   The default is 1

    3703:   The jacobian is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1 or `SNESSetLagJacobianPersists()` was called.

    3705: .seealso: [](ch_snes), `SNES`, `SNESSetLagJacobian()`, `SNESSetLagPreconditioner()`, `SNESGetLagPreconditioner()`, `SNESSetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`

    3707: @*/
    3708: PetscErrorCode SNESGetLagJacobian(SNES snes, PetscInt *lag)
    3709: {
    3710:   PetscFunctionBegin;
    3712:   *lag = snes->lagjacobian;
    3713:   PetscFunctionReturn(PETSC_SUCCESS);
    3714: }

    3716: /*@
    3717:   SNESSetLagJacobianPersists - Set whether or not the Jacobian lagging persists through multiple nonlinear solves

    3719:   Logically collective

    3721:   Input Parameters:
    3722: + snes - the `SNES` context
    3723: - flg  - jacobian lagging persists if true

    3725:   Options Database Keys:
    3726: + -snes_lag_jacobian_persists <true,false>       - sets the persistence through multiple SNES solves
    3727: . -snes_lag_jacobian <-2,1,2,...>                - sets the lag
    3728: . -snes_lag_preconditioner_persists <true,false> - sets the persistence through multiple SNES solves
    3729: - -snes_lag_preconditioner <-2,1,2,...>          - sets the lag

    3731:   Level: advanced

    3733:   Notes:
    3734:   Normally when `SNESSetLagJacobian()` is used, the Jacobian is always rebuilt at the beginning of each new nonlinear solve, this removes that behavior

    3736:   This is useful both for nonlinear preconditioning, where it's appropriate to have the Jacobian be stale by
    3737:   several solves, and for implicit time-stepping, where Jacobian lagging in the inner nonlinear solve over several
    3738:   timesteps may present huge efficiency gains.

    3740: .seealso: [](ch_snes), `SNES`, `SNESSetLagPreconditionerPersists()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESGetNPC()`
    3741: @*/
    3742: PetscErrorCode SNESSetLagJacobianPersists(SNES snes, PetscBool flg)
    3743: {
    3744:   PetscFunctionBegin;
    3747:   snes->lagjac_persist = flg;
    3748:   PetscFunctionReturn(PETSC_SUCCESS);
    3749: }

    3751: /*@
    3752:   SNESSetLagPreconditionerPersists - Set whether or not the preconditioner lagging persists through multiple nonlinear solves

    3754:   Logically Collective

    3756:   Input Parameters:
    3757: + snes - the `SNES` context
    3758: - flg  - preconditioner lagging persists if true

    3760:   Options Database Keys:
    3761: + -snes_lag_jacobian_persists <true,false>       - sets the persistence through multiple SNES solves
    3762: . -snes_lag_jacobian <-2,1,2,...>                - sets the lag
    3763: . -snes_lag_preconditioner_persists <true,false> - sets the persistence through multiple SNES solves
    3764: - -snes_lag_preconditioner <-2,1,2,...>          - sets the lag

    3766:   Level: developer

    3768:   Notes:
    3769:   Normally when `SNESSetLagPreconditioner()` is used, the preconditioner is always rebuilt at the beginning of each new nonlinear solve, this removes that behavior

    3771:   This is useful both for nonlinear preconditioning, where it's appropriate to have the preconditioner be stale
    3772:   by several solves, and for implicit time-stepping, where preconditioner lagging in the inner nonlinear solve over
    3773:   several timesteps may present huge efficiency gains.

    3775: .seealso: [](ch_snes), `SNES`, `SNESSetLagJacobianPersists()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESGetNPC()`, `SNESSetLagPreconditioner()`
    3776: @*/
    3777: PetscErrorCode SNESSetLagPreconditionerPersists(SNES snes, PetscBool flg)
    3778: {
    3779:   PetscFunctionBegin;
    3782:   snes->lagpre_persist = flg;
    3783:   PetscFunctionReturn(PETSC_SUCCESS);
    3784: }

    3786: /*@
    3787:   SNESSetForceIteration - force `SNESSolve()` to take at least one iteration regardless of the initial residual norm

    3789:   Logically Collective

    3791:   Input Parameters:
    3792: + snes  - the `SNES` context
    3793: - force - `PETSC_TRUE` require at least one iteration

    3795:   Options Database Key:
    3796: . -snes_force_iteration <force> - Sets forcing an iteration

    3798:   Level: intermediate

    3800:   Note:
    3801:   This is used sometimes with `TS` to prevent `TS` from detecting a false steady state solution

    3803: .seealso: [](ch_snes), `SNES`, `TS`, `SNESSetDivergenceTolerance()`
    3804: @*/
    3805: PetscErrorCode SNESSetForceIteration(SNES snes, PetscBool force)
    3806: {
    3807:   PetscFunctionBegin;
    3809:   snes->forceiteration = force;
    3810:   PetscFunctionReturn(PETSC_SUCCESS);
    3811: }

    3813: /*@
    3814:   SNESGetForceIteration - Check whether or not `SNESSolve()` take at least one iteration regardless of the initial residual norm

    3816:   Logically Collective

    3818:   Input Parameter:
    3819: . snes - the `SNES` context

    3821:   Output Parameter:
    3822: . force - `PETSC_TRUE` requires at least one iteration.

    3824:   Level: intermediate

    3826: .seealso: [](ch_snes), `SNES`, `SNESSetForceIteration()`, `SNESSetDivergenceTolerance()`
    3827: @*/
    3828: PetscErrorCode SNESGetForceIteration(SNES snes, PetscBool *force)
    3829: {
    3830:   PetscFunctionBegin;
    3832:   *force = snes->forceiteration;
    3833:   PetscFunctionReturn(PETSC_SUCCESS);
    3834: }

    3836: /*@
    3837:   SNESSetTolerances - Sets various parameters used in `SNES` convergence tests.

    3839:   Logically Collective

    3841:   Input Parameters:
    3842: + snes   - the `SNES` context
    3843: . abstol - the absolute convergence tolerance, $ F(x^n) \le abstol $
    3844: . rtol   - the relative convergence tolerance, $ F(x^n) \le reltol * F(x^0) $
    3845: . stol   - convergence tolerance in terms of the norm of the change in the solution between steps,  || delta x || < stol*|| x ||
    3846: . maxit  - the maximum number of iterations allowed in the solver, default 50.
    3847: - maxf   - the maximum number of function evaluations allowed in the solver (use `PETSC_UNLIMITED` indicates no limit), default 10,000

    3849:   Options Database Keys:
    3850: + -snes_atol <abstol>    - Sets `abstol`
    3851: . -snes_rtol <rtol>      - Sets `rtol`
    3852: . -snes_stol <stol>      - Sets `stol`
    3853: . -snes_max_it <maxit>   - Sets `maxit`
    3854: - -snes_max_funcs <maxf> - Sets `maxf` (use `unlimited` to have no maximum)

    3856:   Level: intermediate

    3858:   Note:
    3859:   All parameters must be non-negative

    3861:   Use `PETSC_CURRENT` to retain the current value of any parameter and `PETSC_DETERMINE` to use the default value for the given `SNES`.
    3862:   The default value is the value in the object when its type is set.

    3864:   Use `PETSC_UNLIMITED` on `maxit` or `maxf` to indicate there is no bound on the number of iterations or number of function evaluations.

    3866:   Fortran Note:
    3867:   Use `PETSC_CURRENT_INTEGER`, `PETSC_CURRENT_REAL`, `PETSC_UNLIMITED_INTEGER`, `PETSC_DETERMINE_INTEGER`, or `PETSC_DETERMINE_REAL`

    3869: .seealso: [](ch_snes), `SNESSolve()`, `SNES`, `SNESSetDivergenceTolerance()`, `SNESSetForceIteration()`
    3870: @*/
    3871: PetscErrorCode SNESSetTolerances(SNES snes, PetscReal abstol, PetscReal rtol, PetscReal stol, PetscInt maxit, PetscInt maxf)
    3872: {
    3873:   PetscFunctionBegin;

    3881:   if (abstol == (PetscReal)PETSC_DETERMINE) {
    3882:     snes->abstol = snes->default_abstol;
    3883:   } else if (abstol != (PetscReal)PETSC_CURRENT) {
    3884:     PetscCheck(abstol >= 0.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Absolute tolerance %g must be non-negative", (double)abstol);
    3885:     snes->abstol = abstol;
    3886:   }

    3888:   if (rtol == (PetscReal)PETSC_DETERMINE) {
    3889:     snes->rtol = snes->default_rtol;
    3890:   } else if (rtol != (PetscReal)PETSC_CURRENT) {
    3891:     PetscCheck(rtol >= 0.0 && 1.0 > rtol, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Relative tolerance %g must be non-negative and less than 1.0", (double)rtol);
    3892:     snes->rtol = rtol;
    3893:   }

    3895:   if (stol == (PetscReal)PETSC_DETERMINE) {
    3896:     snes->stol = snes->default_stol;
    3897:   } else if (stol != (PetscReal)PETSC_CURRENT) {
    3898:     PetscCheck(stol >= 0.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Step tolerance %g must be non-negative", (double)stol);
    3899:     snes->stol = stol;
    3900:   }

    3902:   if (maxit == PETSC_DETERMINE) {
    3903:     snes->max_its = snes->default_max_its;
    3904:   } else if (maxit == PETSC_UNLIMITED) {
    3905:     snes->max_its = PETSC_INT_MAX;
    3906:   } else if (maxit != PETSC_CURRENT) {
    3907:     PetscCheck(maxit >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Maximum number of iterations %" PetscInt_FMT " must be non-negative", maxit);
    3908:     snes->max_its = maxit;
    3909:   }

    3911:   if (maxf == PETSC_DETERMINE) {
    3912:     snes->max_funcs = snes->default_max_funcs;
    3913:   } else if (maxf == PETSC_UNLIMITED || maxf == -1) {
    3914:     snes->max_funcs = PETSC_UNLIMITED;
    3915:   } else if (maxf != PETSC_CURRENT) {
    3916:     PetscCheck(maxf >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Maximum number of function evaluations %" PetscInt_FMT " must be nonnegative", maxf);
    3917:     snes->max_funcs = maxf;
    3918:   }
    3919:   PetscFunctionReturn(PETSC_SUCCESS);
    3920: }

    3922: /*@
    3923:   SNESSetDivergenceTolerance - Sets the divergence tolerance used for the `SNES` divergence test.

    3925:   Logically Collective

    3927:   Input Parameters:
    3928: + snes   - the `SNES` context
    3929: - divtol - the divergence tolerance. Use `PETSC_UNLIMITED` to deactivate the test. If the residual norm $ F(x^n) \ge divtol * F(x^0) $ the solver
    3930:            is stopped due to divergence.

    3932:   Options Database Key:
    3933: . -snes_divergence_tolerance <divtol> - Sets `divtol`

    3935:   Level: intermediate

    3937:   Notes:
    3938:   Use `PETSC_DETERMINE` to use the default value from when the object's type was set.

    3940:   Fortran Note:
    3941:   Use ``PETSC_DETERMINE_REAL` or `PETSC_UNLIMITED_REAL`

    3943: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetTolerances()`, `SNESGetDivergenceTolerance()`
    3944: @*/
    3945: PetscErrorCode SNESSetDivergenceTolerance(SNES snes, PetscReal divtol)
    3946: {
    3947:   PetscFunctionBegin;

    3951:   if (divtol == (PetscReal)PETSC_DETERMINE) {
    3952:     snes->divtol = snes->default_divtol;
    3953:   } else if (divtol == (PetscReal)PETSC_UNLIMITED || divtol == -1) {
    3954:     snes->divtol = PETSC_UNLIMITED;
    3955:   } else if (divtol != (PetscReal)PETSC_CURRENT) {
    3956:     PetscCheck(divtol >= 1.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Divergence tolerance %g must be greater than 1.0", (double)divtol);
    3957:     snes->divtol = divtol;
    3958:   }
    3959:   PetscFunctionReturn(PETSC_SUCCESS);
    3960: }

    3962: /*@
    3963:   SNESGetTolerances - Gets various parameters used in `SNES` convergence tests.

    3965:   Not Collective

    3967:   Input Parameter:
    3968: . snes - the `SNES` context

    3970:   Output Parameters:
    3971: + atol  - the absolute convergence tolerance
    3972: . rtol  - the relative convergence tolerance
    3973: . stol  - convergence tolerance in terms of the norm of the change in the solution between steps
    3974: . maxit - the maximum number of iterations allowed
    3975: - maxf  - the maximum number of function evaluations allowed, `PETSC_UNLIMITED` indicates no bound

    3977:   Level: intermediate

    3979:   Notes:
    3980:   See `SNESSetTolerances()` for details on the parameters.

    3982:   The user can specify `NULL` for any parameter that is not needed.

    3984: .seealso: [](ch_snes), `SNES`, `SNESSetTolerances()`
    3985: @*/
    3986: PetscErrorCode SNESGetTolerances(SNES snes, PetscReal *atol, PetscReal *rtol, PetscReal *stol, PetscInt *maxit, PetscInt *maxf)
    3987: {
    3988:   PetscFunctionBegin;
    3990:   if (atol) *atol = snes->abstol;
    3991:   if (rtol) *rtol = snes->rtol;
    3992:   if (stol) *stol = snes->stol;
    3993:   if (maxit) *maxit = snes->max_its;
    3994:   if (maxf) *maxf = snes->max_funcs;
    3995:   PetscFunctionReturn(PETSC_SUCCESS);
    3996: }

    3998: /*@
    3999:   SNESGetDivergenceTolerance - Gets divergence tolerance used in divergence test.

    4001:   Not Collective

    4003:   Input Parameters:
    4004: + snes   - the `SNES` context
    4005: - divtol - divergence tolerance

    4007:   Level: intermediate

    4009: .seealso: [](ch_snes), `SNES`, `SNESSetDivergenceTolerance()`
    4010: @*/
    4011: PetscErrorCode SNESGetDivergenceTolerance(SNES snes, PetscReal *divtol)
    4012: {
    4013:   PetscFunctionBegin;
    4015:   if (divtol) *divtol = snes->divtol;
    4016:   PetscFunctionReturn(PETSC_SUCCESS);
    4017: }

    4019: PETSC_INTERN PetscErrorCode SNESMonitorRange_Private(SNES, PetscInt, PetscReal *);

    4021: PetscErrorCode SNESMonitorLGRange(SNES snes, PetscInt n, PetscReal rnorm, void *monctx)
    4022: {
    4023:   PetscDrawLG      lg;
    4024:   PetscReal        x, y, per;
    4025:   PetscViewer      v = (PetscViewer)monctx;
    4026:   static PetscReal prev; /* should be in the context */
    4027:   PetscDraw        draw;

    4029:   PetscFunctionBegin;
    4031:   PetscCall(PetscViewerDrawGetDrawLG(v, 0, &lg));
    4032:   if (!n) PetscCall(PetscDrawLGReset(lg));
    4033:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4034:   PetscCall(PetscDrawSetTitle(draw, "Residual norm"));
    4035:   x = (PetscReal)n;
    4036:   if (rnorm > 0.0) y = PetscLog10Real(rnorm);
    4037:   else y = -15.0;
    4038:   PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4039:   if (n < 20 || !(n % 5) || snes->reason) {
    4040:     PetscCall(PetscDrawLGDraw(lg));
    4041:     PetscCall(PetscDrawLGSave(lg));
    4042:   }

    4044:   PetscCall(PetscViewerDrawGetDrawLG(v, 1, &lg));
    4045:   if (!n) PetscCall(PetscDrawLGReset(lg));
    4046:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4047:   PetscCall(PetscDrawSetTitle(draw, "% elements > .2*max element"));
    4048:   PetscCall(SNESMonitorRange_Private(snes, n, &per));
    4049:   x = (PetscReal)n;
    4050:   y = 100.0 * per;
    4051:   PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4052:   if (n < 20 || !(n % 5) || snes->reason) {
    4053:     PetscCall(PetscDrawLGDraw(lg));
    4054:     PetscCall(PetscDrawLGSave(lg));
    4055:   }

    4057:   PetscCall(PetscViewerDrawGetDrawLG(v, 2, &lg));
    4058:   if (!n) {
    4059:     prev = rnorm;
    4060:     PetscCall(PetscDrawLGReset(lg));
    4061:   }
    4062:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4063:   PetscCall(PetscDrawSetTitle(draw, "(norm -oldnorm)/oldnorm"));
    4064:   x = (PetscReal)n;
    4065:   y = (prev - rnorm) / prev;
    4066:   PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4067:   if (n < 20 || !(n % 5) || snes->reason) {
    4068:     PetscCall(PetscDrawLGDraw(lg));
    4069:     PetscCall(PetscDrawLGSave(lg));
    4070:   }

    4072:   PetscCall(PetscViewerDrawGetDrawLG(v, 3, &lg));
    4073:   if (!n) PetscCall(PetscDrawLGReset(lg));
    4074:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4075:   PetscCall(PetscDrawSetTitle(draw, "(norm -oldnorm)/oldnorm*(% > .2 max)"));
    4076:   x = (PetscReal)n;
    4077:   y = (prev - rnorm) / (prev * per);
    4078:   if (n > 2) { /*skip initial crazy value */
    4079:     PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4080:   }
    4081:   if (n < 20 || !(n % 5) || snes->reason) {
    4082:     PetscCall(PetscDrawLGDraw(lg));
    4083:     PetscCall(PetscDrawLGSave(lg));
    4084:   }
    4085:   prev = rnorm;
    4086:   PetscFunctionReturn(PETSC_SUCCESS);
    4087: }

    4089: /*@
    4090:   SNESConverged - Run the convergence test and update the `SNESConvergedReason`.

    4092:   Collective

    4094:   Input Parameters:
    4095: + snes  - the `SNES` context
    4096: . it    - current iteration
    4097: . xnorm - 2-norm of current iterate
    4098: . snorm - 2-norm of current step
    4099: - fnorm - 2-norm of function

    4101:   Level: developer

    4103:   Note:
    4104:   This routine is called by the `SNESSolve()` implementations.
    4105:   It does not typically need to be called by the user.

    4107: .seealso: [](ch_snes), `SNES`, `SNESSolve`, `SNESSetConvergenceTest()`, `SNESGetConvergenceTest()`
    4108: @*/
    4109: PetscErrorCode SNESConverged(SNES snes, PetscInt it, PetscReal xnorm, PetscReal snorm, PetscReal fnorm)
    4110: {
    4111:   PetscFunctionBegin;
    4112:   if (!snes->reason) {
    4113:     if (snes->normschedule == SNES_NORM_ALWAYS) PetscUseTypeMethod(snes, converged, it, xnorm, snorm, fnorm, &snes->reason, snes->cnvP);
    4114:     if (it == snes->max_its && !snes->reason) {
    4115:       if (snes->normschedule == SNES_NORM_ALWAYS) {
    4116:         PetscCall(PetscInfo(snes, "Maximum number of iterations has been reached: %" PetscInt_FMT "\n", snes->max_its));
    4117:         snes->reason = SNES_DIVERGED_MAX_IT;
    4118:       } else snes->reason = SNES_CONVERGED_ITS;
    4119:     }
    4120:   }
    4121:   PetscFunctionReturn(PETSC_SUCCESS);
    4122: }

    4124: /*@
    4125:   SNESMonitor - runs any `SNES` monitor routines provided with `SNESMonitor()` or the options database

    4127:   Collective

    4129:   Input Parameters:
    4130: + snes  - nonlinear solver context obtained from `SNESCreate()`
    4131: . iter  - current iteration number
    4132: - rnorm - current relative norm of the residual

    4134:   Level: developer

    4136:   Note:
    4137:   This routine is called by the `SNESSolve()` implementations.
    4138:   It does not typically need to be called by the user.

    4140: .seealso: [](ch_snes), `SNES`, `SNESMonitorSet()`
    4141: @*/
    4142: PetscErrorCode SNESMonitor(SNES snes, PetscInt iter, PetscReal rnorm)
    4143: {
    4144:   PetscInt i, n = snes->numbermonitors;

    4146:   PetscFunctionBegin;
    4147:   if (n > 0) SNESCheckFunctionNorm(snes, rnorm);
    4148:   PetscCall(VecLockReadPush(snes->vec_sol));
    4149:   for (i = 0; i < n; i++) PetscCall((*snes->monitor[i])(snes, iter, rnorm, snes->monitorcontext[i]));
    4150:   PetscCall(VecLockReadPop(snes->vec_sol));
    4151:   PetscFunctionReturn(PETSC_SUCCESS);
    4152: }

    4154: /* ------------ Routines to set performance monitoring options ----------- */

    4156: /*MC
    4157:     SNESMonitorFunction - functional form passed to `SNESMonitorSet()` to monitor convergence of nonlinear solver

    4159:      Synopsis:
    4160: #include <petscsnes.h>
    4161:     PetscErrorCode SNESMonitorFunction(SNES snes, PetscInt its, PetscReal norm, void *mctx)

    4163:      Collective

    4165:     Input Parameters:
    4166: +    snes - the `SNES` context
    4167: .    its - iteration number
    4168: .    norm - 2-norm function value (may be estimated)
    4169: -    mctx - [optional] monitoring context

    4171:    Level: advanced

    4173: .seealso: [](ch_snes), `SNESMonitorSet()`, `SNESMonitorSet()`, `SNESMonitorGet()`
    4174: M*/

    4176: /*@C
    4177:   SNESMonitorSet - Sets an ADDITIONAL function that is to be used at every
    4178:   iteration of the `SNES` nonlinear solver to display the iteration's
    4179:   progress.

    4181:   Logically Collective

    4183:   Input Parameters:
    4184: + snes           - the `SNES` context
    4185: . f              - the monitor function,  for the calling sequence see `SNESMonitorFunction`
    4186: . mctx           - [optional] user-defined context for private data for the monitor routine (use `NULL` if no context is desired)
    4187: - monitordestroy - [optional] routine that frees monitor context (may be `NULL`), see `PetscCtxDestroyFn` for the calling sequence

    4189:   Options Database Keys:
    4190: + -snes_monitor               - sets `SNESMonitorDefault()`
    4191: . -snes_monitor draw::draw_lg - sets line graph monitor,
    4192: - -snes_monitor_cancel        - cancels all monitors that have been hardwired into a code by calls to `SNESMonitorSet()`, but does not cancel those set via
    4193:                                 the options database.

    4195:   Level: intermediate

    4197:   Note:
    4198:   Several different monitoring routines may be set by calling
    4199:   `SNESMonitorSet()` multiple times; all will be called in the
    4200:   order in which they were set.

    4202:   Fortran Note:
    4203:   Only a single monitor function can be set for each `SNES` object

    4205: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESMonitorDefault()`, `SNESMonitorCancel()`, `SNESMonitorFunction`, `PetscCtxDestroyFn`
    4206: @*/
    4207: PetscErrorCode SNESMonitorSet(SNES snes, PetscErrorCode (*f)(SNES, PetscInt, PetscReal, void *), void *mctx, PetscCtxDestroyFn *monitordestroy)
    4208: {
    4209:   PetscInt  i;
    4210:   PetscBool identical;

    4212:   PetscFunctionBegin;
    4214:   for (i = 0; i < snes->numbermonitors; i++) {
    4215:     PetscCall(PetscMonitorCompare((PetscErrorCode (*)(void))f, mctx, monitordestroy, (PetscErrorCode (*)(void))snes->monitor[i], snes->monitorcontext[i], snes->monitordestroy[i], &identical));
    4216:     if (identical) PetscFunctionReturn(PETSC_SUCCESS);
    4217:   }
    4218:   PetscCheck(snes->numbermonitors < MAXSNESMONITORS, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Too many monitors set");
    4219:   snes->monitor[snes->numbermonitors]          = f;
    4220:   snes->monitordestroy[snes->numbermonitors]   = monitordestroy;
    4221:   snes->monitorcontext[snes->numbermonitors++] = mctx;
    4222:   PetscFunctionReturn(PETSC_SUCCESS);
    4223: }

    4225: /*@
    4226:   SNESMonitorCancel - Clears all the monitor functions for a `SNES` object.

    4228:   Logically Collective

    4230:   Input Parameter:
    4231: . snes - the `SNES` context

    4233:   Options Database Key:
    4234: . -snes_monitor_cancel - cancels all monitors that have been hardwired
    4235:                          into a code by calls to `SNESMonitorSet()`, but does not cancel those
    4236:                          set via the options database

    4238:   Level: intermediate

    4240:   Note:
    4241:   There is no way to clear one specific monitor from a `SNES` object.

    4243: .seealso: [](ch_snes), `SNES`, `SNESMonitorGet()`, `SNESMonitorDefault()`, `SNESMonitorSet()`
    4244: @*/
    4245: PetscErrorCode SNESMonitorCancel(SNES snes)
    4246: {
    4247:   PetscInt i;

    4249:   PetscFunctionBegin;
    4251:   for (i = 0; i < snes->numbermonitors; i++) {
    4252:     if (snes->monitordestroy[i]) PetscCall((*snes->monitordestroy[i])(&snes->monitorcontext[i]));
    4253:   }
    4254:   snes->numbermonitors = 0;
    4255:   PetscFunctionReturn(PETSC_SUCCESS);
    4256: }

    4258: /*MC
    4259:     SNESConvergenceTestFunction - functional form used for testing of convergence of nonlinear solver

    4261:      Synopsis:
    4262: #include <petscsnes.h>
    4263:      PetscErrorCode SNESConvergenceTest(SNES snes, PetscInt it, PetscReal xnorm, PetscReal gnorm, PetscReal f, SNESConvergedReason *reason, void *cctx)

    4265:      Collective

    4267:     Input Parameters:
    4268: +    snes - the `SNES` context
    4269: .    it - current iteration (0 is the first and is before any Newton step)
    4270: .    xnorm - 2-norm of current iterate
    4271: .    gnorm - 2-norm of current step
    4272: .    f - 2-norm of function
    4273: -    cctx - [optional] convergence context

    4275:     Output Parameter:
    4276: .    reason - reason for convergence/divergence, only needs to be set when convergence or divergence is detected

    4278:    Level: intermediate

    4280: .seealso: [](ch_snes), `SNES`, `SNESSolve`, `SNESSetConvergenceTest()`, `SNESGetConvergenceTest()`
    4281: M*/

    4283: /*@C
    4284:   SNESSetConvergenceTest - Sets the function that is to be used
    4285:   to test for convergence of the nonlinear iterative solution.

    4287:   Logically Collective

    4289:   Input Parameters:
    4290: + snes                        - the `SNES` context
    4291: . SNESConvergenceTestFunction - routine to test for convergence
    4292: . cctx                        - [optional] context for private data for the convergence routine  (may be `NULL`)
    4293: - destroy                     - [optional] destructor for the context (may be `NULL`; `PETSC_NULL_FUNCTION` in Fortran)

    4295:   Level: advanced

    4297: .seealso: [](ch_snes), `SNES`, `SNESConvergedDefault()`, `SNESConvergedSkip()`, `SNESConvergenceTestFunction`
    4298: @*/
    4299: PetscErrorCode SNESSetConvergenceTest(SNES snes, PetscErrorCode (*SNESConvergenceTestFunction)(SNES, PetscInt, PetscReal, PetscReal, PetscReal, SNESConvergedReason *, void *), void *cctx, PetscErrorCode (*destroy)(void *))
    4300: {
    4301:   PetscFunctionBegin;
    4303:   if (!SNESConvergenceTestFunction) SNESConvergenceTestFunction = SNESConvergedSkip;
    4304:   if (snes->ops->convergeddestroy) PetscCall((*snes->ops->convergeddestroy)(snes->cnvP));
    4305:   snes->ops->converged        = SNESConvergenceTestFunction;
    4306:   snes->ops->convergeddestroy = destroy;
    4307:   snes->cnvP                  = cctx;
    4308:   PetscFunctionReturn(PETSC_SUCCESS);
    4309: }

    4311: /*@
    4312:   SNESGetConvergedReason - Gets the reason the `SNES` iteration was stopped, which may be due to convergence, divergence, or stagnation

    4314:   Not Collective

    4316:   Input Parameter:
    4317: . snes - the `SNES` context

    4319:   Output Parameter:
    4320: . reason - negative value indicates diverged, positive value converged, see `SNESConvergedReason` for the individual convergence tests for complete lists

    4322:   Options Database Key:
    4323: . -snes_converged_reason - prints the reason to standard out

    4325:   Level: intermediate

    4327:   Note:
    4328:   Should only be called after the call the `SNESSolve()` is complete, if it is called earlier it returns the value `SNES__CONVERGED_ITERATING`.

    4330: .seealso: [](ch_snes), `SNESSolve()`, `SNESSetConvergenceTest()`, `SNESSetConvergedReason()`, `SNESConvergedReason`, `SNESGetConvergedReasonString()`
    4331: @*/
    4332: PetscErrorCode SNESGetConvergedReason(SNES snes, SNESConvergedReason *reason)
    4333: {
    4334:   PetscFunctionBegin;
    4336:   PetscAssertPointer(reason, 2);
    4337:   *reason = snes->reason;
    4338:   PetscFunctionReturn(PETSC_SUCCESS);
    4339: }

    4341: /*@C
    4342:   SNESGetConvergedReasonString - Return a human readable string for `SNESConvergedReason`

    4344:   Not Collective

    4346:   Input Parameter:
    4347: . snes - the `SNES` context

    4349:   Output Parameter:
    4350: . strreason - a human readable string that describes `SNES` converged reason

    4352:   Level: beginner

    4354: .seealso: [](ch_snes), `SNES`, `SNESGetConvergedReason()`
    4355: @*/
    4356: PetscErrorCode SNESGetConvergedReasonString(SNES snes, const char **strreason)
    4357: {
    4358:   PetscFunctionBegin;
    4360:   PetscAssertPointer(strreason, 2);
    4361:   *strreason = SNESConvergedReasons[snes->reason];
    4362:   PetscFunctionReturn(PETSC_SUCCESS);
    4363: }

    4365: /*@
    4366:   SNESSetConvergedReason - Sets the reason the `SNES` iteration was stopped.

    4368:   Not Collective

    4370:   Input Parameters:
    4371: + snes   - the `SNES` context
    4372: - reason - negative value indicates diverged, positive value converged, see `SNESConvergedReason` or the
    4373:             manual pages for the individual convergence tests for complete lists

    4375:   Level: developer

    4377:   Developer Note:
    4378:   Called inside the various `SNESSolve()` implementations

    4380: .seealso: [](ch_snes), `SNESGetConvergedReason()`, `SNESSetConvergenceTest()`, `SNESConvergedReason`
    4381: @*/
    4382: PetscErrorCode SNESSetConvergedReason(SNES snes, SNESConvergedReason reason)
    4383: {
    4384:   PetscFunctionBegin;
    4386:   PetscCheck(!snes->errorifnotconverged || reason > 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_PLIB, "SNES code should have previously errored due to negative reason");
    4387:   snes->reason = reason;
    4388:   PetscFunctionReturn(PETSC_SUCCESS);
    4389: }

    4391: /*@
    4392:   SNESSetConvergenceHistory - Sets the arrays used to hold the convergence history.

    4394:   Logically Collective

    4396:   Input Parameters:
    4397: + snes  - iterative context obtained from `SNESCreate()`
    4398: . a     - array to hold history, this array will contain the function norms computed at each step
    4399: . its   - integer array holds the number of linear iterations for each solve.
    4400: . na    - size of `a` and `its`
    4401: - reset - `PETSC_TRUE` indicates each new nonlinear solve resets the history counter to zero,
    4402:           else it continues storing new values for new nonlinear solves after the old ones

    4404:   Level: intermediate

    4406:   Notes:
    4407:   If 'a' and 'its' are `NULL` then space is allocated for the history. If 'na' is `PETSC_DECIDE` (or, deprecated, `PETSC_DEFAULT`) then a
    4408:   default array of length 1,000 is allocated.

    4410:   This routine is useful, e.g., when running a code for purposes
    4411:   of accurate performance monitoring, when no I/O should be done
    4412:   during the section of code that is being timed.

    4414:   If the arrays run out of space after a number of iterations then the later values are not saved in the history

    4416: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESGetConvergenceHistory()`
    4417: @*/
    4418: PetscErrorCode SNESSetConvergenceHistory(SNES snes, PetscReal a[], PetscInt its[], PetscInt na, PetscBool reset)
    4419: {
    4420:   PetscFunctionBegin;
    4422:   if (a) PetscAssertPointer(a, 2);
    4423:   if (its) PetscAssertPointer(its, 3);
    4424:   if (!a) {
    4425:     if (na == PETSC_DECIDE) na = 1000;
    4426:     PetscCall(PetscCalloc2(na, &a, na, &its));
    4427:     snes->conv_hist_alloc = PETSC_TRUE;
    4428:   }
    4429:   snes->conv_hist       = a;
    4430:   snes->conv_hist_its   = its;
    4431:   snes->conv_hist_max   = (size_t)na;
    4432:   snes->conv_hist_len   = 0;
    4433:   snes->conv_hist_reset = reset;
    4434:   PetscFunctionReturn(PETSC_SUCCESS);
    4435: }

    4437: #if defined(PETSC_HAVE_MATLAB)
    4438:   #include <engine.h> /* MATLAB include file */
    4439:   #include <mex.h>    /* MATLAB include file */

    4441: PETSC_EXTERN mxArray *SNESGetConvergenceHistoryMatlab(SNES snes)
    4442: {
    4443:   mxArray   *mat;
    4444:   PetscInt   i;
    4445:   PetscReal *ar;

    4447:   mat = mxCreateDoubleMatrix(snes->conv_hist_len, 1, mxREAL);
    4448:   ar  = (PetscReal *)mxGetData(mat);
    4449:   for (i = 0; i < snes->conv_hist_len; i++) ar[i] = snes->conv_hist[i];
    4450:   return mat;
    4451: }
    4452: #endif

    4454: /*@C
    4455:   SNESGetConvergenceHistory - Gets the arrays used to hold the convergence history.

    4457:   Not Collective

    4459:   Input Parameter:
    4460: . snes - iterative context obtained from `SNESCreate()`

    4462:   Output Parameters:
    4463: + a   - array to hold history, usually was set with `SNESSetConvergenceHistory()`
    4464: . its - integer array holds the number of linear iterations (or
    4465:          negative if not converged) for each solve.
    4466: - na  - size of `a` and `its`

    4468:   Level: intermediate

    4470:   Note:
    4471:   This routine is useful, e.g., when running a code for purposes
    4472:   of accurate performance monitoring, when no I/O should be done
    4473:   during the section of code that is being timed.

    4475:   Fortran Notes:
    4476:   Return the arrays with ``SNESRestoreConvergenceHistory()`

    4478:   Use the arguments
    4479: .vb
    4480:   PetscReal, pointer :: a(:)
    4481:   PetscInt, pointer :: its(:)
    4482: .ve

    4484: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetConvergenceHistory()`
    4485: @*/
    4486: PetscErrorCode SNESGetConvergenceHistory(SNES snes, PetscReal *a[], PetscInt *its[], PetscInt *na)
    4487: {
    4488:   PetscFunctionBegin;
    4490:   if (a) *a = snes->conv_hist;
    4491:   if (its) *its = snes->conv_hist_its;
    4492:   if (na) *na = (PetscInt)snes->conv_hist_len;
    4493:   PetscFunctionReturn(PETSC_SUCCESS);
    4494: }

    4496: /*@C
    4497:   SNESSetUpdate - Sets the general-purpose update function called
    4498:   at the beginning of every iteration of the nonlinear solve. Specifically
    4499:   it is called just before the Jacobian is "evaluated" and after the function
    4500:   evaluation.

    4502:   Logically Collective

    4504:   Input Parameters:
    4505: + snes - The nonlinear solver context
    4506: - func - The update function; for calling sequence see `SNESUpdateFn`

    4508:   Level: advanced

    4510:   Notes:
    4511:   This is NOT what one uses to update the ghost points before a function evaluation, that should be done at the beginning of your function provided
    4512:   to `SNESSetFunction()`, or `SNESSetPicard()`
    4513:   This is not used by most users, and it is intended to provide a general hook that is run
    4514:   right before the direction step is computed.

    4516:   Users are free to modify the current residual vector,
    4517:   the current linearization point, or any other vector associated to the specific solver used.
    4518:   If such modifications take place, it is the user responsibility to update all the relevant
    4519:   vectors. For example, if one is adjusting the model parameters at each Newton step their code may look like
    4520: .vb
    4521:   PetscErrorCode update(SNES snes, PetscInt iteration)
    4522:   {
    4523:     PetscFunctionBeginUser;
    4524:     if (iteration > 0) {
    4525:       // update the model parameters here
    4526:       Vec x,f;
    4527:       PetscCall(SNESGetSolution(snes,&x));
    4528:       PetcCall(SNESGetFunction(snes,&f,NULL,NULL));
    4529:       PetscCall(SNESComputeFunction(snes,x,f));
    4530:     }
    4531:     PetscFunctionReturn(PETSC_SUCCESS);
    4532:   }
    4533: .ve

    4535:   There are a variety of function hooks one many set that are called at different stages of the nonlinear solution process, see the functions listed below.

    4537: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetJacobian()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESNewtonTRSetPreCheck()`, `SNESNewtonTRSetPostCheck()`,
    4538:          `SNESMonitorSet()`
    4539: @*/
    4540: PetscErrorCode SNESSetUpdate(SNES snes, SNESUpdateFn *func)
    4541: {
    4542:   PetscFunctionBegin;
    4544:   snes->ops->update = func;
    4545:   PetscFunctionReturn(PETSC_SUCCESS);
    4546: }

    4548: /*@
    4549:   SNESConvergedReasonView - Displays the reason a `SNES` solve converged or diverged to a viewer

    4551:   Collective

    4553:   Input Parameters:
    4554: + snes   - iterative context obtained from `SNESCreate()`
    4555: - viewer - the viewer to display the reason

    4557:   Options Database Keys:
    4558: + -snes_converged_reason          - print reason for converged or diverged, also prints number of iterations
    4559: - -snes_converged_reason ::failed - only print reason and number of iterations when diverged

    4561:   Level: beginner

    4563:   Note:
    4564:   To change the format of the output call `PetscViewerPushFormat`(viewer,format) before this call. Use `PETSC_VIEWER_DEFAULT` for the default,
    4565:   use `PETSC_VIEWER_FAILED` to only display a reason if it fails.

    4567: .seealso: [](ch_snes), `SNESConvergedReason`, `PetscViewer`, `SNES`,
    4568:           `SNESCreate()`, `SNESSetUp()`, `SNESDestroy()`, `SNESSetTolerances()`, `SNESConvergedDefault()`, `SNESGetConvergedReason()`,
    4569:           `SNESConvergedReasonViewFromOptions()`,
    4570:           `PetscViewerPushFormat()`, `PetscViewerPopFormat()`
    4571: @*/
    4572: PetscErrorCode SNESConvergedReasonView(SNES snes, PetscViewer viewer)
    4573: {
    4574:   PetscViewerFormat format;
    4575:   PetscBool         isAscii;

    4577:   PetscFunctionBegin;
    4578:   if (!viewer) viewer = PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes));
    4579:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isAscii));
    4580:   if (isAscii) {
    4581:     PetscCall(PetscViewerGetFormat(viewer, &format));
    4582:     PetscCall(PetscViewerASCIIAddTab(viewer, ((PetscObject)snes)->tablevel + 1));
    4583:     if (format == PETSC_VIEWER_ASCII_INFO_DETAIL) {
    4584:       DM       dm;
    4585:       Vec      u;
    4586:       PetscDS  prob;
    4587:       PetscInt Nf, f;
    4588:       PetscErrorCode (**exactSol)(PetscInt, PetscReal, const PetscReal[], PetscInt, PetscScalar[], void *);
    4589:       void    **exactCtx;
    4590:       PetscReal error;

    4592:       PetscCall(SNESGetDM(snes, &dm));
    4593:       PetscCall(SNESGetSolution(snes, &u));
    4594:       PetscCall(DMGetDS(dm, &prob));
    4595:       PetscCall(PetscDSGetNumFields(prob, &Nf));
    4596:       PetscCall(PetscMalloc2(Nf, &exactSol, Nf, &exactCtx));
    4597:       for (f = 0; f < Nf; ++f) PetscCall(PetscDSGetExactSolution(prob, f, &exactSol[f], &exactCtx[f]));
    4598:       PetscCall(DMComputeL2Diff(dm, 0.0, exactSol, exactCtx, u, &error));
    4599:       PetscCall(PetscFree2(exactSol, exactCtx));
    4600:       if (error < 1.0e-11) PetscCall(PetscViewerASCIIPrintf(viewer, "L_2 Error: < 1.0e-11\n"));
    4601:       else PetscCall(PetscViewerASCIIPrintf(viewer, "L_2 Error: %g\n", (double)error));
    4602:     }
    4603:     if (snes->reason > 0 && format != PETSC_VIEWER_FAILED) {
    4604:       if (((PetscObject)snes)->prefix) {
    4605:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear %s solve converged due to %s iterations %" PetscInt_FMT "\n", ((PetscObject)snes)->prefix, SNESConvergedReasons[snes->reason], snes->iter));
    4606:       } else {
    4607:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear solve converged due to %s iterations %" PetscInt_FMT "\n", SNESConvergedReasons[snes->reason], snes->iter));
    4608:       }
    4609:     } else if (snes->reason <= 0) {
    4610:       if (((PetscObject)snes)->prefix) {
    4611:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear %s solve did not converge due to %s iterations %" PetscInt_FMT "\n", ((PetscObject)snes)->prefix, SNESConvergedReasons[snes->reason], snes->iter));
    4612:       } else {
    4613:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear solve did not converge due to %s iterations %" PetscInt_FMT "\n", SNESConvergedReasons[snes->reason], snes->iter));
    4614:       }
    4615:     }
    4616:     PetscCall(PetscViewerASCIISubtractTab(viewer, ((PetscObject)snes)->tablevel + 1));
    4617:   }
    4618:   PetscFunctionReturn(PETSC_SUCCESS);
    4619: }

    4621: /*@C
    4622:   SNESConvergedReasonViewSet - Sets an ADDITIONAL function that is to be used at the
    4623:   end of the nonlinear solver to display the convergence reason of the nonlinear solver.

    4625:   Logically Collective

    4627:   Input Parameters:
    4628: + snes              - the `SNES` context
    4629: . f                 - the `SNESConvergedReason` view function
    4630: . vctx              - [optional] user-defined context for private data for the `SNESConvergedReason` view function (use `NULL` if no context is desired)
    4631: - reasonviewdestroy - [optional] routine that frees the context (may be `NULL`), see `PetscCtxDestroyFn` for the calling sequence

    4633:   Calling sequence of `f`:
    4634: + snes - the `SNES` context
    4635: - vctx - [optional] context for private data for the function

    4637:   Options Database Keys:
    4638: + -snes_converged_reason             - sets a default `SNESConvergedReasonView()`
    4639: - -snes_converged_reason_view_cancel - cancels all converged reason viewers that have been hardwired into a code by
    4640:                                        calls to `SNESConvergedReasonViewSet()`, but does not cancel those set via the options database.

    4642:   Level: intermediate

    4644:   Note:
    4645:   Several different converged reason view routines may be set by calling
    4646:   `SNESConvergedReasonViewSet()` multiple times; all will be called in the
    4647:   order in which they were set.

    4649: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESConvergedReason`, `SNESGetConvergedReason()`, `SNESConvergedReasonView()`, `SNESConvergedReasonViewCancel()`,
    4650:           `PetscCtxDestroyFn`
    4651: @*/
    4652: PetscErrorCode SNESConvergedReasonViewSet(SNES snes, PetscErrorCode (*f)(SNES snes, void *vctx), void *vctx, PetscCtxDestroyFn *reasonviewdestroy)
    4653: {
    4654:   PetscInt  i;
    4655:   PetscBool identical;

    4657:   PetscFunctionBegin;
    4659:   for (i = 0; i < snes->numberreasonviews; i++) {
    4660:     PetscCall(PetscMonitorCompare((PetscErrorCode (*)(void))f, vctx, reasonviewdestroy, (PetscErrorCode (*)(void))snes->reasonview[i], snes->reasonviewcontext[i], snes->reasonviewdestroy[i], &identical));
    4661:     if (identical) PetscFunctionReturn(PETSC_SUCCESS);
    4662:   }
    4663:   PetscCheck(snes->numberreasonviews < MAXSNESREASONVIEWS, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Too many SNES reasonview set");
    4664:   snes->reasonview[snes->numberreasonviews]          = f;
    4665:   snes->reasonviewdestroy[snes->numberreasonviews]   = reasonviewdestroy;
    4666:   snes->reasonviewcontext[snes->numberreasonviews++] = vctx;
    4667:   PetscFunctionReturn(PETSC_SUCCESS);
    4668: }

    4670: /*@
    4671:   SNESConvergedReasonViewFromOptions - Processes command line options to determine if/how a `SNESConvergedReason` is to be viewed at the end of `SNESSolve()`
    4672:   All the user-provided viewer routines set with `SNESConvergedReasonViewSet()` will be called, if they exist.

    4674:   Collective

    4676:   Input Parameter:
    4677: . snes - the `SNES` object

    4679:   Level: advanced

    4681: .seealso: [](ch_snes), `SNES`, `SNESConvergedReason`, `SNESConvergedReasonViewSet()`, `SNESCreate()`, `SNESSetUp()`, `SNESDestroy()`,
    4682:           `SNESSetTolerances()`, `SNESConvergedDefault()`, `SNESGetConvergedReason()`, `SNESConvergedReasonView()`
    4683: @*/
    4684: PetscErrorCode SNESConvergedReasonViewFromOptions(SNES snes)
    4685: {
    4686:   static PetscBool incall = PETSC_FALSE;

    4688:   PetscFunctionBegin;
    4689:   if (incall) PetscFunctionReturn(PETSC_SUCCESS);
    4690:   incall = PETSC_TRUE;

    4692:   /* All user-provided viewers are called first, if they exist. */
    4693:   for (PetscInt i = 0; i < snes->numberreasonviews; i++) PetscCall((*snes->reasonview[i])(snes, snes->reasonviewcontext[i]));

    4695:   /* Call PETSc default routine if users ask for it */
    4696:   if (snes->convergedreasonviewer) {
    4697:     PetscCall(PetscViewerPushFormat(snes->convergedreasonviewer, snes->convergedreasonformat));
    4698:     PetscCall(SNESConvergedReasonView(snes, snes->convergedreasonviewer));
    4699:     PetscCall(PetscViewerPopFormat(snes->convergedreasonviewer));
    4700:   }
    4701:   incall = PETSC_FALSE;
    4702:   PetscFunctionReturn(PETSC_SUCCESS);
    4703: }

    4705: /*@
    4706:   SNESSolve - Solves a nonlinear system $F(x) = b $ associated with a `SNES` object

    4708:   Collective

    4710:   Input Parameters:
    4711: + snes - the `SNES` context
    4712: . b    - the constant part of the equation $F(x) = b$, or `NULL` to use zero.
    4713: - x    - the solution vector.

    4715:   Level: beginner

    4717:   Note:
    4718:   The user should initialize the vector, `x`, with the initial guess
    4719:   for the nonlinear solve prior to calling `SNESSolve()` .

    4721: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESDestroy()`, `SNESSetFunction()`, `SNESSetJacobian()`, `SNESSetGridSequence()`, `SNESGetSolution()`,
    4722:           `SNESNewtonTRSetPreCheck()`, `SNESNewtonTRGetPreCheck()`, `SNESNewtonTRSetPostCheck()`, `SNESNewtonTRGetPostCheck()`,
    4723:           `SNESLineSearchSetPostCheck()`, `SNESLineSearchGetPostCheck()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchGetPreCheck()`
    4724: @*/
    4725: PetscErrorCode SNESSolve(SNES snes, Vec b, Vec x)
    4726: {
    4727:   PetscBool flg;
    4728:   PetscInt  grid;
    4729:   Vec       xcreated = NULL;
    4730:   DM        dm;

    4732:   PetscFunctionBegin;
    4735:   if (x) PetscCheckSameComm(snes, 1, x, 3);
    4737:   if (b) PetscCheckSameComm(snes, 1, b, 2);

    4739:   /* High level operations using the nonlinear solver */
    4740:   {
    4741:     PetscViewer       viewer;
    4742:     PetscViewerFormat format;
    4743:     PetscInt          num;
    4744:     PetscBool         flg;
    4745:     static PetscBool  incall = PETSC_FALSE;

    4747:     if (!incall) {
    4748:       /* Estimate the convergence rate of the discretization */
    4749:       PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_convergence_estimate", &viewer, &format, &flg));
    4750:       if (flg) {
    4751:         PetscConvEst conv;
    4752:         DM           dm;
    4753:         PetscReal   *alpha; /* Convergence rate of the solution error for each field in the L_2 norm */
    4754:         PetscInt     Nf;

    4756:         incall = PETSC_TRUE;
    4757:         PetscCall(SNESGetDM(snes, &dm));
    4758:         PetscCall(DMGetNumFields(dm, &Nf));
    4759:         PetscCall(PetscCalloc1(Nf, &alpha));
    4760:         PetscCall(PetscConvEstCreate(PetscObjectComm((PetscObject)snes), &conv));
    4761:         PetscCall(PetscConvEstSetSolver(conv, (PetscObject)snes));
    4762:         PetscCall(PetscConvEstSetFromOptions(conv));
    4763:         PetscCall(PetscConvEstSetUp(conv));
    4764:         PetscCall(PetscConvEstGetConvRate(conv, alpha));
    4765:         PetscCall(PetscViewerPushFormat(viewer, format));
    4766:         PetscCall(PetscConvEstRateView(conv, alpha, viewer));
    4767:         PetscCall(PetscViewerPopFormat(viewer));
    4768:         PetscCall(PetscViewerDestroy(&viewer));
    4769:         PetscCall(PetscConvEstDestroy(&conv));
    4770:         PetscCall(PetscFree(alpha));
    4771:         incall = PETSC_FALSE;
    4772:       }
    4773:       /* Adaptively refine the initial grid */
    4774:       num = 1;
    4775:       PetscCall(PetscOptionsGetInt(NULL, ((PetscObject)snes)->prefix, "-snes_adapt_initial", &num, &flg));
    4776:       if (flg) {
    4777:         DMAdaptor adaptor;

    4779:         incall = PETSC_TRUE;
    4780:         PetscCall(DMAdaptorCreate(PetscObjectComm((PetscObject)snes), &adaptor));
    4781:         PetscCall(DMAdaptorSetSolver(adaptor, snes));
    4782:         PetscCall(DMAdaptorSetSequenceLength(adaptor, num));
    4783:         PetscCall(DMAdaptorSetFromOptions(adaptor));
    4784:         PetscCall(DMAdaptorSetUp(adaptor));
    4785:         PetscCall(DMAdaptorAdapt(adaptor, x, DM_ADAPTATION_INITIAL, &dm, &x));
    4786:         PetscCall(DMAdaptorDestroy(&adaptor));
    4787:         incall = PETSC_FALSE;
    4788:       }
    4789:       /* Use grid sequencing to adapt */
    4790:       num = 0;
    4791:       PetscCall(PetscOptionsGetInt(NULL, ((PetscObject)snes)->prefix, "-snes_adapt_sequence", &num, NULL));
    4792:       if (num) {
    4793:         DMAdaptor   adaptor;
    4794:         const char *prefix;

    4796:         incall = PETSC_TRUE;
    4797:         PetscCall(DMAdaptorCreate(PetscObjectComm((PetscObject)snes), &adaptor));
    4798:         PetscCall(SNESGetOptionsPrefix(snes, &prefix));
    4799:         PetscCall(DMAdaptorSetOptionsPrefix(adaptor, prefix));
    4800:         PetscCall(DMAdaptorSetSolver(adaptor, snes));
    4801:         PetscCall(DMAdaptorSetSequenceLength(adaptor, num));
    4802:         PetscCall(DMAdaptorSetFromOptions(adaptor));
    4803:         PetscCall(DMAdaptorSetUp(adaptor));
    4804:         PetscCall(PetscObjectViewFromOptions((PetscObject)adaptor, NULL, "-snes_adapt_view"));
    4805:         PetscCall(DMAdaptorAdapt(adaptor, x, DM_ADAPTATION_SEQUENTIAL, &dm, &x));
    4806:         PetscCall(DMAdaptorDestroy(&adaptor));
    4807:         incall = PETSC_FALSE;
    4808:       }
    4809:     }
    4810:   }
    4811:   if (!x) x = snes->vec_sol;
    4812:   if (!x) {
    4813:     PetscCall(SNESGetDM(snes, &dm));
    4814:     PetscCall(DMCreateGlobalVector(dm, &xcreated));
    4815:     x = xcreated;
    4816:   }
    4817:   PetscCall(SNESViewFromOptions(snes, NULL, "-snes_view_pre"));

    4819:   for (grid = 0; grid < snes->gridsequence; grid++) PetscCall(PetscViewerASCIIPushTab(PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes))));
    4820:   for (grid = 0; grid < snes->gridsequence + 1; grid++) {
    4821:     /* set solution vector */
    4822:     if (!grid) PetscCall(PetscObjectReference((PetscObject)x));
    4823:     PetscCall(VecDestroy(&snes->vec_sol));
    4824:     snes->vec_sol = x;
    4825:     PetscCall(SNESGetDM(snes, &dm));

    4827:     /* set affine vector if provided */
    4828:     if (b) PetscCall(PetscObjectReference((PetscObject)b));
    4829:     PetscCall(VecDestroy(&snes->vec_rhs));
    4830:     snes->vec_rhs = b;

    4832:     if (snes->vec_rhs) PetscCheck(snes->vec_func != snes->vec_rhs, PETSC_COMM_SELF, PETSC_ERR_ARG_IDN, "Right hand side vector cannot be function vector");
    4833:     PetscCheck(snes->vec_func != snes->vec_sol, PETSC_COMM_SELF, PETSC_ERR_ARG_IDN, "Solution vector cannot be function vector");
    4834:     PetscCheck(snes->vec_rhs != snes->vec_sol, PETSC_COMM_SELF, PETSC_ERR_ARG_IDN, "Solution vector cannot be right-hand side vector");
    4835:     if (!snes->vec_sol_update /* && snes->vec_sol */) PetscCall(VecDuplicate(snes->vec_sol, &snes->vec_sol_update));
    4836:     PetscCall(DMShellSetGlobalVector(dm, snes->vec_sol));
    4837:     PetscCall(SNESSetUp(snes));

    4839:     if (!grid) {
    4840:       if (snes->ops->computeinitialguess) PetscCallBack("SNES callback compute initial guess", (*snes->ops->computeinitialguess)(snes, snes->vec_sol, snes->initialguessP));
    4841:     }

    4843:     if (snes->conv_hist_reset) snes->conv_hist_len = 0;
    4844:     PetscCall(SNESResetCounters(snes));
    4845:     snes->reason = SNES_CONVERGED_ITERATING;
    4846:     PetscCall(PetscLogEventBegin(SNES_Solve, snes, 0, 0, 0));
    4847:     PetscUseTypeMethod(snes, solve);
    4848:     PetscCall(PetscLogEventEnd(SNES_Solve, snes, 0, 0, 0));
    4849:     PetscCheck(snes->reason, PETSC_COMM_SELF, PETSC_ERR_PLIB, "Internal error, solver %s returned without setting converged reason", ((PetscObject)snes)->type_name);
    4850:     snes->domainerror = PETSC_FALSE; /* clear the flag if it has been set */

    4852:     if (snes->lagjac_persist) snes->jac_iter += snes->iter;
    4853:     if (snes->lagpre_persist) snes->pre_iter += snes->iter;

    4855:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_test_local_min", NULL, NULL, &flg));
    4856:     if (flg && !PetscPreLoadingOn) PetscCall(SNESTestLocalMin(snes));
    4857:     /* Call converged reason views. This may involve user-provided viewers as well */
    4858:     PetscCall(SNESConvergedReasonViewFromOptions(snes));

    4860:     if (snes->errorifnotconverged) PetscCheck(snes->reason >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_NOT_CONVERGED, "SNESSolve has not converged");
    4861:     if (snes->reason < 0) break;
    4862:     if (grid < snes->gridsequence) {
    4863:       DM  fine;
    4864:       Vec xnew;
    4865:       Mat interp;

    4867:       PetscCall(DMRefine(snes->dm, PetscObjectComm((PetscObject)snes), &fine));
    4868:       PetscCheck(fine, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_INCOMP, "DMRefine() did not perform any refinement, cannot continue grid sequencing");
    4869:       PetscCall(DMGetCoordinatesLocalSetUp(fine));
    4870:       PetscCall(DMCreateInterpolation(snes->dm, fine, &interp, NULL));
    4871:       PetscCall(DMCreateGlobalVector(fine, &xnew));
    4872:       PetscCall(MatInterpolate(interp, x, xnew));
    4873:       PetscCall(DMInterpolate(snes->dm, interp, fine));
    4874:       PetscCall(MatDestroy(&interp));
    4875:       x = xnew;

    4877:       PetscCall(SNESReset(snes));
    4878:       PetscCall(SNESSetDM(snes, fine));
    4879:       PetscCall(SNESResetFromOptions(snes));
    4880:       PetscCall(DMDestroy(&fine));
    4881:       PetscCall(PetscViewerASCIIPopTab(PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes))));
    4882:     }
    4883:   }
    4884:   PetscCall(SNESViewFromOptions(snes, NULL, "-snes_view"));
    4885:   PetscCall(VecViewFromOptions(snes->vec_sol, (PetscObject)snes, "-snes_view_solution"));
    4886:   PetscCall(DMMonitor(snes->dm));
    4887:   PetscCall(SNESMonitorPauseFinal_Internal(snes));

    4889:   PetscCall(VecDestroy(&xcreated));
    4890:   PetscCall(PetscObjectSAWsBlock((PetscObject)snes));
    4891:   PetscFunctionReturn(PETSC_SUCCESS);
    4892: }

    4894: /* --------- Internal routines for SNES Package --------- */

    4896: /*@
    4897:   SNESSetType - Sets the algorithm/method to be used to solve the nonlinear system with the given `SNES`

    4899:   Collective

    4901:   Input Parameters:
    4902: + snes - the `SNES` context
    4903: - type - a known method

    4905:   Options Database Key:
    4906: . -snes_type <type> - Sets the method; use -help for a list
    4907:    of available methods (for instance, newtonls or newtontr)

    4909:   Level: intermediate

    4911:   Notes:
    4912:   See `SNESType` for available methods (for instance)
    4913: +    `SNESNEWTONLS` - Newton's method with line search
    4914:   (systems of nonlinear equations)
    4915: -    `SNESNEWTONTR` - Newton's method with trust region
    4916:   (systems of nonlinear equations)

    4918:   Normally, it is best to use the `SNESSetFromOptions()` command and then
    4919:   set the `SNES` solver type from the options database rather than by using
    4920:   this routine.  Using the options database provides the user with
    4921:   maximum flexibility in evaluating the many nonlinear solvers.
    4922:   The `SNESSetType()` routine is provided for those situations where it
    4923:   is necessary to set the nonlinear solver independently of the command
    4924:   line or options database.  This might be the case, for example, when
    4925:   the choice of solver changes during the execution of the program,
    4926:   and the user's application is taking responsibility for choosing the
    4927:   appropriate method.

    4929:   Developer Note:
    4930:   `SNESRegister()` adds a constructor for a new `SNESType` to `SNESList`, `SNESSetType()` locates
    4931:   the constructor in that list and calls it to create the specific object.

    4933: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESType`, `SNESCreate()`, `SNESDestroy()`, `SNESGetType()`, `SNESSetFromOptions()`
    4934: @*/
    4935: PetscErrorCode SNESSetType(SNES snes, SNESType type)
    4936: {
    4937:   PetscBool match;
    4938:   PetscErrorCode (*r)(SNES);

    4940:   PetscFunctionBegin;
    4942:   PetscAssertPointer(type, 2);

    4944:   PetscCall(PetscObjectTypeCompare((PetscObject)snes, type, &match));
    4945:   if (match) PetscFunctionReturn(PETSC_SUCCESS);

    4947:   PetscCall(PetscFunctionListFind(SNESList, type, &r));
    4948:   PetscCheck(r, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_UNKNOWN_TYPE, "Unable to find requested SNES type %s", type);
    4949:   /* Destroy the previous private SNES context */
    4950:   PetscTryTypeMethod(snes, destroy);
    4951:   /* Reinitialize function pointers in SNESOps structure */
    4952:   snes->ops->setup          = NULL;
    4953:   snes->ops->solve          = NULL;
    4954:   snes->ops->view           = NULL;
    4955:   snes->ops->setfromoptions = NULL;
    4956:   snes->ops->destroy        = NULL;

    4958:   /* It may happen the user has customized the line search before calling SNESSetType */
    4959:   if (((PetscObject)snes)->type_name) PetscCall(SNESLineSearchDestroy(&snes->linesearch));

    4961:   /* Call the SNESCreate_XXX routine for this particular Nonlinear solver */
    4962:   snes->setupcalled = PETSC_FALSE;

    4964:   PetscCall(PetscObjectChangeTypeName((PetscObject)snes, type));
    4965:   PetscCall((*r)(snes));
    4966:   PetscFunctionReturn(PETSC_SUCCESS);
    4967: }

    4969: /*@
    4970:   SNESGetType - Gets the `SNES` method type and name (as a string).

    4972:   Not Collective

    4974:   Input Parameter:
    4975: . snes - nonlinear solver context

    4977:   Output Parameter:
    4978: . type - `SNES` method (a character string)

    4980:   Level: intermediate

    4982: .seealso: [](ch_snes), `SNESSetType()`, `SNESType`, `SNESSetFromOptions()`, `SNES`
    4983: @*/
    4984: PetscErrorCode SNESGetType(SNES snes, SNESType *type)
    4985: {
    4986:   PetscFunctionBegin;
    4988:   PetscAssertPointer(type, 2);
    4989:   *type = ((PetscObject)snes)->type_name;
    4990:   PetscFunctionReturn(PETSC_SUCCESS);
    4991: }

    4993: /*@
    4994:   SNESSetSolution - Sets the solution vector for use by the `SNES` routines.

    4996:   Logically Collective

    4998:   Input Parameters:
    4999: + snes - the `SNES` context obtained from `SNESCreate()`
    5000: - u    - the solution vector

    5002:   Level: beginner

    5004: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESGetSolution()`, `Vec`
    5005: @*/
    5006: PetscErrorCode SNESSetSolution(SNES snes, Vec u)
    5007: {
    5008:   DM dm;

    5010:   PetscFunctionBegin;
    5013:   PetscCall(PetscObjectReference((PetscObject)u));
    5014:   PetscCall(VecDestroy(&snes->vec_sol));

    5016:   snes->vec_sol = u;

    5018:   PetscCall(SNESGetDM(snes, &dm));
    5019:   PetscCall(DMShellSetGlobalVector(dm, u));
    5020:   PetscFunctionReturn(PETSC_SUCCESS);
    5021: }

    5023: /*@
    5024:   SNESGetSolution - Returns the vector where the approximate solution is
    5025:   stored. This is the fine grid solution when using `SNESSetGridSequence()`.

    5027:   Not Collective, but `x` is parallel if `snes` is parallel

    5029:   Input Parameter:
    5030: . snes - the `SNES` context

    5032:   Output Parameter:
    5033: . x - the solution

    5035:   Level: intermediate

    5037: .seealso: [](ch_snes), `SNESSetSolution()`, `SNESSolve()`, `SNES`, `SNESGetSolutionUpdate()`, `SNESGetFunction()`
    5038: @*/
    5039: PetscErrorCode SNESGetSolution(SNES snes, Vec *x)
    5040: {
    5041:   PetscFunctionBegin;
    5043:   PetscAssertPointer(x, 2);
    5044:   *x = snes->vec_sol;
    5045:   PetscFunctionReturn(PETSC_SUCCESS);
    5046: }

    5048: /*@
    5049:   SNESGetSolutionUpdate - Returns the vector where the solution update is
    5050:   stored.

    5052:   Not Collective, but `x` is parallel if `snes` is parallel

    5054:   Input Parameter:
    5055: . snes - the `SNES` context

    5057:   Output Parameter:
    5058: . x - the solution update

    5060:   Level: advanced

    5062: .seealso: [](ch_snes), `SNES`, `SNESGetSolution()`, `SNESGetFunction()`
    5063: @*/
    5064: PetscErrorCode SNESGetSolutionUpdate(SNES snes, Vec *x)
    5065: {
    5066:   PetscFunctionBegin;
    5068:   PetscAssertPointer(x, 2);
    5069:   *x = snes->vec_sol_update;
    5070:   PetscFunctionReturn(PETSC_SUCCESS);
    5071: }

    5073: /*@C
    5074:   SNESGetFunction - Returns the function that defines the nonlinear system set with `SNESSetFunction()`

    5076:   Not Collective, but `r` is parallel if `snes` is parallel. Collective if `r` is requested, but has not been created yet.

    5078:   Input Parameter:
    5079: . snes - the `SNES` context

    5081:   Output Parameters:
    5082: + r   - the vector that is used to store residuals (or `NULL` if you don't want it)
    5083: . f   - the function (or `NULL` if you don't want it);  for calling sequence see `SNESFunctionFn`
    5084: - ctx - the function context (or `NULL` if you don't want it)

    5086:   Level: advanced

    5088:   Note:
    5089:   The vector `r` DOES NOT, in general, contain the current value of the `SNES` nonlinear function

    5091: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetFunction()`, `SNESGetSolution()`, `SNESFunctionFn`
    5092: @*/
    5093: PetscErrorCode SNESGetFunction(SNES snes, Vec *r, SNESFunctionFn **f, void **ctx)
    5094: {
    5095:   DM dm;

    5097:   PetscFunctionBegin;
    5099:   if (r) {
    5100:     if (!snes->vec_func) {
    5101:       if (snes->vec_rhs) {
    5102:         PetscCall(VecDuplicate(snes->vec_rhs, &snes->vec_func));
    5103:       } else if (snes->vec_sol) {
    5104:         PetscCall(VecDuplicate(snes->vec_sol, &snes->vec_func));
    5105:       } else if (snes->dm) {
    5106:         PetscCall(DMCreateGlobalVector(snes->dm, &snes->vec_func));
    5107:       }
    5108:     }
    5109:     *r = snes->vec_func;
    5110:   }
    5111:   PetscCall(SNESGetDM(snes, &dm));
    5112:   PetscCall(DMSNESGetFunction(dm, f, ctx));
    5113:   PetscFunctionReturn(PETSC_SUCCESS);
    5114: }

    5116: /*@C
    5117:   SNESGetNGS - Returns the function and context set with `SNESSetNGS()`

    5119:   Input Parameter:
    5120: . snes - the `SNES` context

    5122:   Output Parameters:
    5123: + f   - the function (or `NULL`) see `SNESNGSFn` for calling sequence
    5124: - ctx - the function context (or `NULL`)

    5126:   Level: advanced

    5128: .seealso: [](ch_snes), `SNESSetNGS()`, `SNESGetFunction()`, `SNESNGSFn`
    5129: @*/
    5130: PetscErrorCode SNESGetNGS(SNES snes, SNESNGSFn **f, void **ctx)
    5131: {
    5132:   DM dm;

    5134:   PetscFunctionBegin;
    5136:   PetscCall(SNESGetDM(snes, &dm));
    5137:   PetscCall(DMSNESGetNGS(dm, f, ctx));
    5138:   PetscFunctionReturn(PETSC_SUCCESS);
    5139: }

    5141: /*@
    5142:   SNESSetOptionsPrefix - Sets the prefix used for searching for all
    5143:   `SNES` options in the database.

    5145:   Logically Collective

    5147:   Input Parameters:
    5148: + snes   - the `SNES` context
    5149: - prefix - the prefix to prepend to all option names

    5151:   Level: advanced

    5153:   Note:
    5154:   A hyphen (-) must NOT be given at the beginning of the prefix name.
    5155:   The first character of all runtime options is AUTOMATICALLY the hyphen.

    5157: .seealso: [](ch_snes), `SNES`, `SNESSetFromOptions()`, `SNESAppendOptionsPrefix()`
    5158: @*/
    5159: PetscErrorCode SNESSetOptionsPrefix(SNES snes, const char prefix[])
    5160: {
    5161:   PetscFunctionBegin;
    5163:   PetscCall(PetscObjectSetOptionsPrefix((PetscObject)snes, prefix));
    5164:   if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));
    5165:   if (snes->linesearch) {
    5166:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    5167:     PetscCall(PetscObjectSetOptionsPrefix((PetscObject)snes->linesearch, prefix));
    5168:   }
    5169:   PetscCall(KSPSetOptionsPrefix(snes->ksp, prefix));
    5170:   PetscFunctionReturn(PETSC_SUCCESS);
    5171: }

    5173: /*@
    5174:   SNESAppendOptionsPrefix - Appends to the prefix used for searching for all
    5175:   `SNES` options in the database.

    5177:   Logically Collective

    5179:   Input Parameters:
    5180: + snes   - the `SNES` context
    5181: - prefix - the prefix to prepend to all option names

    5183:   Level: advanced

    5185:   Note:
    5186:   A hyphen (-) must NOT be given at the beginning of the prefix name.
    5187:   The first character of all runtime options is AUTOMATICALLY the hyphen.

    5189: .seealso: [](ch_snes), `SNESGetOptionsPrefix()`, `SNESSetOptionsPrefix()`
    5190: @*/
    5191: PetscErrorCode SNESAppendOptionsPrefix(SNES snes, const char prefix[])
    5192: {
    5193:   PetscFunctionBegin;
    5195:   PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)snes, prefix));
    5196:   if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));
    5197:   if (snes->linesearch) {
    5198:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    5199:     PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)snes->linesearch, prefix));
    5200:   }
    5201:   PetscCall(KSPAppendOptionsPrefix(snes->ksp, prefix));
    5202:   PetscFunctionReturn(PETSC_SUCCESS);
    5203: }

    5205: /*@
    5206:   SNESGetOptionsPrefix - Gets the prefix used for searching for all
    5207:   `SNES` options in the database.

    5209:   Not Collective

    5211:   Input Parameter:
    5212: . snes - the `SNES` context

    5214:   Output Parameter:
    5215: . prefix - pointer to the prefix string used

    5217:   Level: advanced

    5219:   Fortran Note:
    5220:   The user should pass in a string 'prefix' of
    5221:   sufficient length to hold the prefix.

    5223: .seealso: [](ch_snes), `SNES`, `SNESSetOptionsPrefix()`, `SNESAppendOptionsPrefix()`
    5224: @*/
    5225: PetscErrorCode SNESGetOptionsPrefix(SNES snes, const char *prefix[])
    5226: {
    5227:   PetscFunctionBegin;
    5229:   PetscCall(PetscObjectGetOptionsPrefix((PetscObject)snes, prefix));
    5230:   PetscFunctionReturn(PETSC_SUCCESS);
    5231: }

    5233: /*@C
    5234:   SNESRegister - Adds a method to the nonlinear solver package.

    5236:   Not Collective

    5238:   Input Parameters:
    5239: + sname    - name of a new user-defined solver
    5240: - function - routine to create method context

    5242:   Level: advanced

    5244:   Note:
    5245:   `SNESRegister()` may be called multiple times to add several user-defined solvers.

    5247:   Example Usage:
    5248: .vb
    5249:    SNESRegister("my_solver", MySolverCreate);
    5250: .ve

    5252:   Then, your solver can be chosen with the procedural interface via
    5253: $     SNESSetType(snes, "my_solver")
    5254:   or at runtime via the option
    5255: $     -snes_type my_solver

    5257: .seealso: [](ch_snes), `SNESRegisterAll()`, `SNESRegisterDestroy()`
    5258: @*/
    5259: PetscErrorCode SNESRegister(const char sname[], PetscErrorCode (*function)(SNES))
    5260: {
    5261:   PetscFunctionBegin;
    5262:   PetscCall(SNESInitializePackage());
    5263:   PetscCall(PetscFunctionListAdd(&SNESList, sname, function));
    5264:   PetscFunctionReturn(PETSC_SUCCESS);
    5265: }

    5267: PetscErrorCode SNESTestLocalMin(SNES snes)
    5268: {
    5269:   PetscInt    N, i, j;
    5270:   Vec         u, uh, fh;
    5271:   PetscScalar value;
    5272:   PetscReal   norm;

    5274:   PetscFunctionBegin;
    5275:   PetscCall(SNESGetSolution(snes, &u));
    5276:   PetscCall(VecDuplicate(u, &uh));
    5277:   PetscCall(VecDuplicate(u, &fh));

    5279:   /* currently only works for sequential */
    5280:   PetscCall(PetscPrintf(PetscObjectComm((PetscObject)snes), "Testing FormFunction() for local min\n"));
    5281:   PetscCall(VecGetSize(u, &N));
    5282:   for (i = 0; i < N; i++) {
    5283:     PetscCall(VecCopy(u, uh));
    5284:     PetscCall(PetscPrintf(PetscObjectComm((PetscObject)snes), "i = %" PetscInt_FMT "\n", i));
    5285:     for (j = -10; j < 11; j++) {
    5286:       value = PetscSign(j) * PetscExpReal(PetscAbs(j) - 10.0);
    5287:       PetscCall(VecSetValue(uh, i, value, ADD_VALUES));
    5288:       PetscCall(SNESComputeFunction(snes, uh, fh));
    5289:       PetscCall(VecNorm(fh, NORM_2, &norm));
    5290:       PetscCall(PetscPrintf(PetscObjectComm((PetscObject)snes), "       j norm %" PetscInt_FMT " %18.16e\n", j, (double)norm));
    5291:       value = -value;
    5292:       PetscCall(VecSetValue(uh, i, value, ADD_VALUES));
    5293:     }
    5294:   }
    5295:   PetscCall(VecDestroy(&uh));
    5296:   PetscCall(VecDestroy(&fh));
    5297:   PetscFunctionReturn(PETSC_SUCCESS);
    5298: }

    5300: /*@
    5301:   SNESKSPSetUseEW - Sets `SNES` to the use Eisenstat-Walker method for
    5302:   computing relative tolerance for linear solvers within an inexact
    5303:   Newton method.

    5305:   Logically Collective

    5307:   Input Parameters:
    5308: + snes - `SNES` context
    5309: - flag - `PETSC_TRUE` or `PETSC_FALSE`

    5311:   Options Database Keys:
    5312: + -snes_ksp_ew                       - use Eisenstat-Walker method for determining linear system convergence
    5313: . -snes_ksp_ew_version ver           - version of  Eisenstat-Walker method
    5314: . -snes_ksp_ew_rtol0 <rtol0>         - Sets rtol0
    5315: . -snes_ksp_ew_rtolmax <rtolmax>     - Sets rtolmax
    5316: . -snes_ksp_ew_gamma <gamma>         - Sets gamma
    5317: . -snes_ksp_ew_alpha <alpha>         - Sets alpha
    5318: . -snes_ksp_ew_alpha2 <alpha2>       - Sets alpha2
    5319: - -snes_ksp_ew_threshold <threshold> - Sets threshold

    5321:   Level: advanced

    5323:   Note:
    5324:   The default is to use a constant relative tolerance for
    5325:   the inner linear solvers.  Alternatively, one can use the
    5326:   Eisenstat-Walker method {cite}`ew96`, where the relative convergence tolerance
    5327:   is reset at each Newton iteration according progress of the nonlinear
    5328:   solver.

    5330: .seealso: [](ch_snes), `KSP`, `SNES`, `SNESKSPGetUseEW()`, `SNESKSPGetParametersEW()`, `SNESKSPSetParametersEW()`
    5331: @*/
    5332: PetscErrorCode SNESKSPSetUseEW(SNES snes, PetscBool flag)
    5333: {
    5334:   PetscFunctionBegin;
    5337:   snes->ksp_ewconv = flag;
    5338:   PetscFunctionReturn(PETSC_SUCCESS);
    5339: }

    5341: /*@
    5342:   SNESKSPGetUseEW - Gets if `SNES` is using Eisenstat-Walker method
    5343:   for computing relative tolerance for linear solvers within an
    5344:   inexact Newton method.

    5346:   Not Collective

    5348:   Input Parameter:
    5349: . snes - `SNES` context

    5351:   Output Parameter:
    5352: . flag - `PETSC_TRUE` or `PETSC_FALSE`

    5354:   Level: advanced

    5356: .seealso: [](ch_snes), `SNESKSPSetUseEW()`, `SNESKSPGetParametersEW()`, `SNESKSPSetParametersEW()`
    5357: @*/
    5358: PetscErrorCode SNESKSPGetUseEW(SNES snes, PetscBool *flag)
    5359: {
    5360:   PetscFunctionBegin;
    5362:   PetscAssertPointer(flag, 2);
    5363:   *flag = snes->ksp_ewconv;
    5364:   PetscFunctionReturn(PETSC_SUCCESS);
    5365: }

    5367: /*@
    5368:   SNESKSPSetParametersEW - Sets parameters for Eisenstat-Walker
    5369:   convergence criteria for the linear solvers within an inexact
    5370:   Newton method.

    5372:   Logically Collective

    5374:   Input Parameters:
    5375: + snes      - `SNES` context
    5376: . version   - version 1, 2 (default is 2), 3 or 4
    5377: . rtol_0    - initial relative tolerance (0 <= rtol_0 < 1)
    5378: . rtol_max  - maximum relative tolerance (0 <= rtol_max < 1)
    5379: . gamma     - multiplicative factor for version 2 rtol computation
    5380:              (0 <= gamma2 <= 1)
    5381: . alpha     - power for version 2 rtol computation (1 < alpha <= 2)
    5382: . alpha2    - power for safeguard
    5383: - threshold - threshold for imposing safeguard (0 < threshold < 1)

    5385:   Level: advanced

    5387:   Notes:
    5388:   Version 3 was contributed by Luis Chacon, June 2006.

    5390:   Use `PETSC_CURRENT` to retain the default for any of the parameters.

    5392: .seealso: [](ch_snes), `SNES`, `SNESKSPSetUseEW()`, `SNESKSPGetUseEW()`, `SNESKSPGetParametersEW()`
    5393: @*/
    5394: PetscErrorCode SNESKSPSetParametersEW(SNES snes, PetscInt version, PetscReal rtol_0, PetscReal rtol_max, PetscReal gamma, PetscReal alpha, PetscReal alpha2, PetscReal threshold)
    5395: {
    5396:   SNESKSPEW *kctx;

    5398:   PetscFunctionBegin;
    5400:   kctx = (SNESKSPEW *)snes->kspconvctx;
    5401:   PetscCheck(kctx, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "No Eisenstat-Walker context existing");

    5410:   if (version != PETSC_CURRENT) kctx->version = version;
    5411:   if (rtol_0 != (PetscReal)PETSC_CURRENT) kctx->rtol_0 = rtol_0;
    5412:   if (rtol_max != (PetscReal)PETSC_CURRENT) kctx->rtol_max = rtol_max;
    5413:   if (gamma != (PetscReal)PETSC_CURRENT) kctx->gamma = gamma;
    5414:   if (alpha != (PetscReal)PETSC_CURRENT) kctx->alpha = alpha;
    5415:   if (alpha2 != (PetscReal)PETSC_CURRENT) kctx->alpha2 = alpha2;
    5416:   if (threshold != (PetscReal)PETSC_CURRENT) kctx->threshold = threshold;

    5418:   PetscCheck(kctx->version >= 1 && kctx->version <= 4, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Only versions 1 to 4 are supported: %" PetscInt_FMT, kctx->version);
    5419:   PetscCheck(kctx->rtol_0 >= 0.0 && kctx->rtol_0 < 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 <= rtol_0 < 1.0: %g", (double)kctx->rtol_0);
    5420:   PetscCheck(kctx->rtol_max >= 0.0 && kctx->rtol_max < 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 <= rtol_max (%g) < 1.0", (double)kctx->rtol_max);
    5421:   PetscCheck(kctx->gamma >= 0.0 && kctx->gamma <= 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 <= gamma (%g) <= 1.0", (double)kctx->gamma);
    5422:   PetscCheck(kctx->alpha > 1.0 && kctx->alpha <= 2.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "1.0 < alpha (%g) <= 2.0", (double)kctx->alpha);
    5423:   PetscCheck(kctx->threshold > 0.0 && kctx->threshold < 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 < threshold (%g) < 1.0", (double)kctx->threshold);
    5424:   PetscFunctionReturn(PETSC_SUCCESS);
    5425: }

    5427: /*@
    5428:   SNESKSPGetParametersEW - Gets parameters for Eisenstat-Walker
    5429:   convergence criteria for the linear solvers within an inexact
    5430:   Newton method.

    5432:   Not Collective

    5434:   Input Parameter:
    5435: . snes - `SNES` context

    5437:   Output Parameters:
    5438: + version   - version 1, 2 (default is 2), 3 or 4
    5439: . rtol_0    - initial relative tolerance (0 <= rtol_0 < 1)
    5440: . rtol_max  - maximum relative tolerance (0 <= rtol_max < 1)
    5441: . gamma     - multiplicative factor for version 2 rtol computation (0 <= gamma2 <= 1)
    5442: . alpha     - power for version 2 rtol computation (1 < alpha <= 2)
    5443: . alpha2    - power for safeguard
    5444: - threshold - threshold for imposing safeguard (0 < threshold < 1)

    5446:   Level: advanced

    5448: .seealso: [](ch_snes), `SNES`, `SNESKSPSetUseEW()`, `SNESKSPGetUseEW()`, `SNESKSPSetParametersEW()`
    5449: @*/
    5450: PetscErrorCode SNESKSPGetParametersEW(SNES snes, PetscInt *version, PetscReal *rtol_0, PetscReal *rtol_max, PetscReal *gamma, PetscReal *alpha, PetscReal *alpha2, PetscReal *threshold)
    5451: {
    5452:   SNESKSPEW *kctx;

    5454:   PetscFunctionBegin;
    5456:   kctx = (SNESKSPEW *)snes->kspconvctx;
    5457:   PetscCheck(kctx, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "No Eisenstat-Walker context existing");
    5458:   if (version) *version = kctx->version;
    5459:   if (rtol_0) *rtol_0 = kctx->rtol_0;
    5460:   if (rtol_max) *rtol_max = kctx->rtol_max;
    5461:   if (gamma) *gamma = kctx->gamma;
    5462:   if (alpha) *alpha = kctx->alpha;
    5463:   if (alpha2) *alpha2 = kctx->alpha2;
    5464:   if (threshold) *threshold = kctx->threshold;
    5465:   PetscFunctionReturn(PETSC_SUCCESS);
    5466: }

    5468: PetscErrorCode KSPPreSolve_SNESEW(KSP ksp, Vec b, Vec x, void *ctx)
    5469: {
    5470:   SNES       snes = (SNES)ctx;
    5471:   SNESKSPEW *kctx = (SNESKSPEW *)snes->kspconvctx;
    5472:   PetscReal  rtol = PETSC_CURRENT, stol;

    5474:   PetscFunctionBegin;
    5475:   if (!snes->ksp_ewconv) PetscFunctionReturn(PETSC_SUCCESS);
    5476:   if (!snes->iter) {
    5477:     rtol = kctx->rtol_0; /* first time in, so use the original user rtol */
    5478:     PetscCall(VecNorm(snes->vec_func, NORM_2, &kctx->norm_first));
    5479:   } else {
    5480:     PetscCheck(kctx->version >= 1 && kctx->version <= 4, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Only versions 1-4 are supported: %" PetscInt_FMT, kctx->version);
    5481:     if (kctx->version == 1) {
    5482:       rtol = PetscAbsReal(snes->norm - kctx->lresid_last) / kctx->norm_last;
    5483:       stol = PetscPowReal(kctx->rtol_last, kctx->alpha2);
    5484:       if (stol > kctx->threshold) rtol = PetscMax(rtol, stol);
    5485:     } else if (kctx->version == 2) {
    5486:       rtol = kctx->gamma * PetscPowReal(snes->norm / kctx->norm_last, kctx->alpha);
    5487:       stol = kctx->gamma * PetscPowReal(kctx->rtol_last, kctx->alpha);
    5488:       if (stol > kctx->threshold) rtol = PetscMax(rtol, stol);
    5489:     } else if (kctx->version == 3) { /* contributed by Luis Chacon, June 2006. */
    5490:       rtol = kctx->gamma * PetscPowReal(snes->norm / kctx->norm_last, kctx->alpha);
    5491:       /* safeguard: avoid sharp decrease of rtol */
    5492:       stol = kctx->gamma * PetscPowReal(kctx->rtol_last, kctx->alpha);
    5493:       stol = PetscMax(rtol, stol);
    5494:       rtol = PetscMin(kctx->rtol_0, stol);
    5495:       /* safeguard: avoid oversolving */
    5496:       stol = kctx->gamma * (kctx->norm_first * snes->rtol) / snes->norm;
    5497:       stol = PetscMax(rtol, stol);
    5498:       rtol = PetscMin(kctx->rtol_0, stol);
    5499:     } else /* if (kctx->version == 4) */ {
    5500:       /* H.-B. An et al. Journal of Computational and Applied Mathematics 200 (2007) 47-60 */
    5501:       PetscReal ared = PetscAbsReal(kctx->norm_last - snes->norm);
    5502:       PetscReal pred = PetscAbsReal(kctx->norm_last - kctx->lresid_last);
    5503:       PetscReal rk   = ared / pred;
    5504:       if (rk < kctx->v4_p1) rtol = 1. - 2. * kctx->v4_p1;
    5505:       else if (rk < kctx->v4_p2) rtol = kctx->rtol_last;
    5506:       else if (rk < kctx->v4_p3) rtol = kctx->v4_m1 * kctx->rtol_last;
    5507:       else rtol = kctx->v4_m2 * kctx->rtol_last;

    5509:       if (kctx->rtol_last_2 > kctx->v4_m3 && kctx->rtol_last > kctx->v4_m3 && kctx->rk_last_2 < kctx->v4_p1 && kctx->rk_last < kctx->v4_p1) rtol = kctx->v4_m4 * kctx->rtol_last;
    5510:       kctx->rtol_last_2 = kctx->rtol_last;
    5511:       kctx->rk_last_2   = kctx->rk_last;
    5512:       kctx->rk_last     = rk;
    5513:     }
    5514:   }
    5515:   /* safeguard: avoid rtol greater than rtol_max */
    5516:   rtol = PetscMin(rtol, kctx->rtol_max);
    5517:   PetscCall(KSPSetTolerances(ksp, rtol, PETSC_CURRENT, PETSC_CURRENT, PETSC_CURRENT));
    5518:   PetscCall(PetscInfo(snes, "iter %" PetscInt_FMT ", Eisenstat-Walker (version %" PetscInt_FMT ") KSP rtol=%g\n", snes->iter, kctx->version, (double)rtol));
    5519:   PetscFunctionReturn(PETSC_SUCCESS);
    5520: }

    5522: PetscErrorCode KSPPostSolve_SNESEW(KSP ksp, Vec b, Vec x, void *ctx)
    5523: {
    5524:   SNES       snes = (SNES)ctx;
    5525:   SNESKSPEW *kctx = (SNESKSPEW *)snes->kspconvctx;
    5526:   PCSide     pcside;
    5527:   Vec        lres;

    5529:   PetscFunctionBegin;
    5530:   if (!snes->ksp_ewconv) PetscFunctionReturn(PETSC_SUCCESS);
    5531:   PetscCall(KSPGetTolerances(ksp, &kctx->rtol_last, NULL, NULL, NULL));
    5532:   kctx->norm_last = snes->norm;
    5533:   if (kctx->version == 1 || kctx->version == 4) {
    5534:     PC        pc;
    5535:     PetscBool getRes;

    5537:     PetscCall(KSPGetPC(ksp, &pc));
    5538:     PetscCall(PetscObjectTypeCompare((PetscObject)pc, PCNONE, &getRes));
    5539:     if (!getRes) {
    5540:       KSPNormType normtype;

    5542:       PetscCall(KSPGetNormType(ksp, &normtype));
    5543:       getRes = (PetscBool)(normtype == KSP_NORM_UNPRECONDITIONED);
    5544:     }
    5545:     PetscCall(KSPGetPCSide(ksp, &pcside));
    5546:     if (pcside == PC_RIGHT || getRes) { /* KSP residual is true linear residual */
    5547:       PetscCall(KSPGetResidualNorm(ksp, &kctx->lresid_last));
    5548:     } else {
    5549:       /* KSP residual is preconditioned residual */
    5550:       /* compute true linear residual norm */
    5551:       Mat J;
    5552:       PetscCall(KSPGetOperators(ksp, &J, NULL));
    5553:       PetscCall(VecDuplicate(b, &lres));
    5554:       PetscCall(MatMult(J, x, lres));
    5555:       PetscCall(VecAYPX(lres, -1.0, b));
    5556:       PetscCall(VecNorm(lres, NORM_2, &kctx->lresid_last));
    5557:       PetscCall(VecDestroy(&lres));
    5558:     }
    5559:   }
    5560:   PetscFunctionReturn(PETSC_SUCCESS);
    5561: }

    5563: /*@
    5564:   SNESGetKSP - Returns the `KSP` context for a `SNES` solver.

    5566:   Not Collective, but if `snes` is parallel, then `ksp` is parallel

    5568:   Input Parameter:
    5569: . snes - the `SNES` context

    5571:   Output Parameter:
    5572: . ksp - the `KSP` context

    5574:   Level: beginner

    5576:   Notes:
    5577:   The user can then directly manipulate the `KSP` context to set various
    5578:   options, etc.  Likewise, the user can then extract and manipulate the
    5579:   `PC` contexts as well.

    5581:   Some `SNESType`s do not use a `KSP` but a `KSP` is still returned by this function, changes to that `KSP` will have no effect.

    5583: .seealso: [](ch_snes), `SNES`, `KSP`, `PC`, `KSPGetPC()`, `SNESCreate()`, `KSPCreate()`, `SNESSetKSP()`
    5584: @*/
    5585: PetscErrorCode SNESGetKSP(SNES snes, KSP *ksp)
    5586: {
    5587:   PetscFunctionBegin;
    5589:   PetscAssertPointer(ksp, 2);

    5591:   if (!snes->ksp) {
    5592:     PetscCall(KSPCreate(PetscObjectComm((PetscObject)snes), &snes->ksp));
    5593:     PetscCall(PetscObjectIncrementTabLevel((PetscObject)snes->ksp, (PetscObject)snes, 1));

    5595:     PetscCall(KSPSetPreSolve(snes->ksp, KSPPreSolve_SNESEW, snes));
    5596:     PetscCall(KSPSetPostSolve(snes->ksp, KSPPostSolve_SNESEW, snes));

    5598:     PetscCall(KSPMonitorSetFromOptions(snes->ksp, "-snes_monitor_ksp", "snes_preconditioned_residual", snes));
    5599:     PetscCall(PetscObjectSetOptions((PetscObject)snes->ksp, ((PetscObject)snes)->options));
    5600:   }
    5601:   *ksp = snes->ksp;
    5602:   PetscFunctionReturn(PETSC_SUCCESS);
    5603: }

    5605: #include <petsc/private/dmimpl.h>
    5606: /*@
    5607:   SNESSetDM - Sets the `DM` that may be used by some `SNES` nonlinear solvers or their underlying preconditioners

    5609:   Logically Collective

    5611:   Input Parameters:
    5612: + snes - the nonlinear solver context
    5613: - dm   - the `DM`, cannot be `NULL`

    5615:   Level: intermediate

    5617:   Note:
    5618:   A `DM` can only be used for solving one problem at a time because information about the problem is stored on the `DM`,
    5619:   even when not using interfaces like `DMSNESSetFunction()`.  Use `DMClone()` to get a distinct `DM` when solving different
    5620:   problems using the same function space.

    5622: .seealso: [](ch_snes), `DM`, `SNES`, `SNESGetDM()`, `KSPSetDM()`, `KSPGetDM()`
    5623: @*/
    5624: PetscErrorCode SNESSetDM(SNES snes, DM dm)
    5625: {
    5626:   KSP    ksp;
    5627:   DMSNES sdm;

    5629:   PetscFunctionBegin;
    5632:   PetscCall(PetscObjectReference((PetscObject)dm));
    5633:   if (snes->dm) { /* Move the DMSNES context over to the new DM unless the new DM already has one */
    5634:     if (snes->dm->dmsnes && !dm->dmsnes) {
    5635:       PetscCall(DMCopyDMSNES(snes->dm, dm));
    5636:       PetscCall(DMGetDMSNES(snes->dm, &sdm));
    5637:       if (sdm->originaldm == snes->dm) sdm->originaldm = dm; /* Grant write privileges to the replacement DM */
    5638:     }
    5639:     PetscCall(DMCoarsenHookRemove(snes->dm, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, snes));
    5640:     PetscCall(DMDestroy(&snes->dm));
    5641:   }
    5642:   snes->dm     = dm;
    5643:   snes->dmAuto = PETSC_FALSE;

    5645:   PetscCall(SNESGetKSP(snes, &ksp));
    5646:   PetscCall(KSPSetDM(ksp, dm));
    5647:   PetscCall(KSPSetDMActive(ksp, PETSC_FALSE));
    5648:   if (snes->npc) {
    5649:     PetscCall(SNESSetDM(snes->npc, snes->dm));
    5650:     PetscCall(SNESSetNPCSide(snes, snes->npcside));
    5651:   }
    5652:   PetscFunctionReturn(PETSC_SUCCESS);
    5653: }

    5655: /*@
    5656:   SNESGetDM - Gets the `DM` that may be used by some `SNES` nonlinear solvers/preconditioners

    5658:   Not Collective but `dm` obtained is parallel on `snes`

    5660:   Input Parameter:
    5661: . snes - the `SNES` context

    5663:   Output Parameter:
    5664: . dm - the `DM`

    5666:   Level: intermediate

    5668: .seealso: [](ch_snes), `DM`, `SNES`, `SNESSetDM()`, `KSPSetDM()`, `KSPGetDM()`
    5669: @*/
    5670: PetscErrorCode SNESGetDM(SNES snes, DM *dm)
    5671: {
    5672:   PetscFunctionBegin;
    5674:   if (!snes->dm) {
    5675:     PetscCall(DMShellCreate(PetscObjectComm((PetscObject)snes), &snes->dm));
    5676:     snes->dmAuto = PETSC_TRUE;
    5677:   }
    5678:   *dm = snes->dm;
    5679:   PetscFunctionReturn(PETSC_SUCCESS);
    5680: }

    5682: /*@
    5683:   SNESSetNPC - Sets the nonlinear preconditioner to be used.

    5685:   Collective

    5687:   Input Parameters:
    5688: + snes - iterative context obtained from `SNESCreate()`
    5689: - npc  - the `SNES` nonlinear preconditioner object

    5691:   Options Database Key:
    5692: . -npc_snes_type <type> - set the type of the `SNES` to use as the nonlinear preconditioner

    5694:   Level: developer

    5696:   Notes:
    5697:   This is rarely used, rather use `SNESGetNPC()` to retrieve the preconditioner and configure it using the API.

    5699:   Only some `SNESType` can use a nonlinear preconditioner

    5701: .seealso: [](ch_snes), `SNES`, `SNESNGS`, `SNESFAS`, `SNESGetNPC()`, `SNESHasNPC()`
    5702: @*/
    5703: PetscErrorCode SNESSetNPC(SNES snes, SNES npc)
    5704: {
    5705:   PetscFunctionBegin;
    5708:   PetscCheckSameComm(snes, 1, npc, 2);
    5709:   PetscCall(PetscObjectReference((PetscObject)npc));
    5710:   PetscCall(SNESDestroy(&snes->npc));
    5711:   snes->npc = npc;
    5712:   PetscFunctionReturn(PETSC_SUCCESS);
    5713: }

    5715: /*@
    5716:   SNESGetNPC - Gets a nonlinear preconditioning solver SNES` to be used to precondition the original nonlinear solver.

    5718:   Not Collective; but any changes to the obtained the `pc` object must be applied collectively

    5720:   Input Parameter:
    5721: . snes - iterative context obtained from `SNESCreate()`

    5723:   Output Parameter:
    5724: . pc - the `SNES` preconditioner context

    5726:   Options Database Key:
    5727: . -npc_snes_type <type> - set the type of the `SNES` to use as the nonlinear preconditioner

    5729:   Level: advanced

    5731:   Notes:
    5732:   If a `SNES` was previously set with `SNESSetNPC()` then that value is returned, otherwise a new `SNES` object is created that will
    5733:   be used as the nonlinear preconditioner for the current `SNES`.

    5735:   The (preconditioner) `SNES` returned automatically inherits the same nonlinear function and Jacobian supplied to the original
    5736:   `SNES`. These may be overwritten if needed.

    5738:   Use the options database prefixes `-npc_snes`, `-npc_ksp`, etc., to control the configuration of the nonlinear preconditioner

    5740: .seealso: [](ch_snes), `SNESSetNPC()`, `SNESHasNPC()`, `SNES`, `SNESCreate()`
    5741: @*/
    5742: PetscErrorCode SNESGetNPC(SNES snes, SNES *pc)
    5743: {
    5744:   const char *optionsprefix;

    5746:   PetscFunctionBegin;
    5748:   PetscAssertPointer(pc, 2);
    5749:   if (!snes->npc) {
    5750:     void *ctx;

    5752:     PetscCall(SNESCreate(PetscObjectComm((PetscObject)snes), &snes->npc));
    5753:     PetscCall(PetscObjectIncrementTabLevel((PetscObject)snes->npc, (PetscObject)snes, 1));
    5754:     PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    5755:     PetscCall(SNESSetOptionsPrefix(snes->npc, optionsprefix));
    5756:     PetscCall(SNESAppendOptionsPrefix(snes->npc, "npc_"));
    5757:     if (snes->ops->usercompute) {
    5758:       PetscCall(SNESSetComputeApplicationContext(snes, snes->ops->usercompute, snes->ops->ctxdestroy));
    5759:     } else {
    5760:       PetscCall(SNESGetApplicationContext(snes, &ctx));
    5761:       PetscCall(SNESSetApplicationContext(snes->npc, ctx));
    5762:     }
    5763:     PetscCall(SNESSetCountersReset(snes->npc, PETSC_FALSE));
    5764:   }
    5765:   *pc = snes->npc;
    5766:   PetscFunctionReturn(PETSC_SUCCESS);
    5767: }

    5769: /*@
    5770:   SNESHasNPC - Returns whether a nonlinear preconditioner is associated with the given `SNES`

    5772:   Not Collective

    5774:   Input Parameter:
    5775: . snes - iterative context obtained from `SNESCreate()`

    5777:   Output Parameter:
    5778: . has_npc - whether the `SNES` has a nonlinear preconditioner or not

    5780:   Level: developer

    5782: .seealso: [](ch_snes), `SNESSetNPC()`, `SNESGetNPC()`
    5783: @*/
    5784: PetscErrorCode SNESHasNPC(SNES snes, PetscBool *has_npc)
    5785: {
    5786:   PetscFunctionBegin;
    5788:   PetscAssertPointer(has_npc, 2);
    5789:   *has_npc = snes->npc ? PETSC_TRUE : PETSC_FALSE;
    5790:   PetscFunctionReturn(PETSC_SUCCESS);
    5791: }

    5793: /*@
    5794:   SNESSetNPCSide - Sets the nonlinear preconditioning side used by the nonlinear preconditioner inside `SNES`.

    5796:   Logically Collective

    5798:   Input Parameter:
    5799: . snes - iterative context obtained from `SNESCreate()`

    5801:   Output Parameter:
    5802: . side - the preconditioning side, where side is one of
    5803: .vb
    5804:       PC_LEFT  - left preconditioning
    5805:       PC_RIGHT - right preconditioning (default for most nonlinear solvers)
    5806: .ve

    5808:   Options Database Key:
    5809: . -snes_npc_side <right,left> - nonlinear preconditioner side

    5811:   Level: intermediate

    5813:   Note:
    5814:   `SNESNRICHARDSON` and `SNESNCG` only support left preconditioning.

    5816: .seealso: [](ch_snes), `SNES`, `SNESGetNPC()`, `SNESNRICHARDSON`, `SNESNCG`, `SNESType`, `SNESGetNPCSide()`, `KSPSetPCSide()`, `PC_LEFT`, `PC_RIGHT`, `PCSide`
    5817: @*/
    5818: PetscErrorCode SNESSetNPCSide(SNES snes, PCSide side)
    5819: {
    5820:   PetscFunctionBegin;
    5823:   if (side == PC_SIDE_DEFAULT) side = PC_RIGHT;
    5824:   PetscCheck((side == PC_LEFT) || (side == PC_RIGHT), PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_WRONG, "Only PC_LEFT and PC_RIGHT are supported");
    5825:   snes->npcside = side;
    5826:   PetscFunctionReturn(PETSC_SUCCESS);
    5827: }

    5829: /*@
    5830:   SNESGetNPCSide - Gets the preconditioning side used by the nonlinear preconditioner inside `SNES`.

    5832:   Not Collective

    5834:   Input Parameter:
    5835: . snes - iterative context obtained from `SNESCreate()`

    5837:   Output Parameter:
    5838: . side - the preconditioning side, where side is one of
    5839: .vb
    5840:       `PC_LEFT` - left preconditioning
    5841:       `PC_RIGHT` - right preconditioning (default for most nonlinear solvers)
    5842: .ve

    5844:   Level: intermediate

    5846: .seealso: [](ch_snes), `SNES`, `SNESGetNPC()`, `SNESSetNPCSide()`, `KSPGetPCSide()`, `PC_LEFT`, `PC_RIGHT`, `PCSide`
    5847: @*/
    5848: PetscErrorCode SNESGetNPCSide(SNES snes, PCSide *side)
    5849: {
    5850:   PetscFunctionBegin;
    5852:   PetscAssertPointer(side, 2);
    5853:   *side = snes->npcside;
    5854:   PetscFunctionReturn(PETSC_SUCCESS);
    5855: }

    5857: /*@
    5858:   SNESSetLineSearch - Sets the `SNESLineSearch` to be used for a given `SNES`

    5860:   Collective

    5862:   Input Parameters:
    5863: + snes       - iterative context obtained from `SNESCreate()`
    5864: - linesearch - the linesearch object

    5866:   Level: developer

    5868:   Note:
    5869:   This is almost never used, rather one uses `SNESGetLineSearch()` to retrieve the line search and set options on it
    5870:   to configure it using the API).

    5872: .seealso: [](ch_snes), `SNES`, `SNESLineSearch`, `SNESGetLineSearch()`
    5873: @*/
    5874: PetscErrorCode SNESSetLineSearch(SNES snes, SNESLineSearch linesearch)
    5875: {
    5876:   PetscFunctionBegin;
    5879:   PetscCheckSameComm(snes, 1, linesearch, 2);
    5880:   PetscCall(PetscObjectReference((PetscObject)linesearch));
    5881:   PetscCall(SNESLineSearchDestroy(&snes->linesearch));

    5883:   snes->linesearch = linesearch;
    5884:   PetscFunctionReturn(PETSC_SUCCESS);
    5885: }

    5887: /*@
    5888:   SNESGetLineSearch - Returns the line search associated with the `SNES`.

    5890:   Not Collective

    5892:   Input Parameter:
    5893: . snes - iterative context obtained from `SNESCreate()`

    5895:   Output Parameter:
    5896: . linesearch - linesearch context

    5898:   Level: beginner

    5900:   Notes:
    5901:   It creates a default line search instance which can be configured as needed in case it has not been already set with `SNESSetLineSearch()`.

    5903:   You can also use the options database keys `-snes_linesearch_*` to configure the line search. See `SNESLineSearchSetFromOptions()` for the possible options.

    5905: .seealso: [](ch_snes), `SNESLineSearch`, `SNESSetLineSearch()`, `SNESLineSearchCreate()`, `SNESLineSearchSetFromOptions()`
    5906: @*/
    5907: PetscErrorCode SNESGetLineSearch(SNES snes, SNESLineSearch *linesearch)
    5908: {
    5909:   const char *optionsprefix;

    5911:   PetscFunctionBegin;
    5913:   PetscAssertPointer(linesearch, 2);
    5914:   if (!snes->linesearch) {
    5915:     PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    5916:     PetscCall(SNESLineSearchCreate(PetscObjectComm((PetscObject)snes), &snes->linesearch));
    5917:     PetscCall(SNESLineSearchSetSNES(snes->linesearch, snes));
    5918:     PetscCall(SNESLineSearchAppendOptionsPrefix(snes->linesearch, optionsprefix));
    5919:     PetscCall(PetscObjectIncrementTabLevel((PetscObject)snes->linesearch, (PetscObject)snes, 1));
    5920:   }
    5921:   *linesearch = snes->linesearch;
    5922:   PetscFunctionReturn(PETSC_SUCCESS);
    5923: }