Date: 2022-08-02T03:14:40+00:00

Actual source code: gmres.c

      2: /*
      3:     This file implements GMRES (a Generalized Minimal Residual) method.
      4:     Reference:  Saad and Schultz, 1986.

      6:     Some comments on left vs. right preconditioning, and restarts.
      7:     Left and right preconditioning.
      8:     If right preconditioning is chosen, then the problem being solved
      9:     by gmres is actually
     10:        My =  AB^-1 y = f
     11:     so the initial residual is
     12:           r = f - Mx
     13:     Note that B^-1 y = x or y = B x, and if x is non-zero, the initial
     14:     residual is
     15:           r = f - A x
     16:     The final solution is then
     17:           x = B^-1 y

     19:     If left preconditioning is chosen, then the problem being solved is
     20:        My = B^-1 A x = B^-1 f,
     21:     and the initial residual is
     22:        r  = B^-1(f - Ax)

     24:     Restarts:  Restarts are basically solves with x0 not equal to zero.
     25:     Note that we can eliminate an extra application of B^-1 between
     26:     restarts as long as we don't require that the solution at the end
     27:     of an unsuccessful gmres iteration always be the solution x.
     28:  */

     30: #include <../src/ksp/ksp/impls/gmres/gmresimpl.h>
     31: #define GMRES_DELTA_DIRECTIONS 10
     32: #define GMRES_DEFAULT_MAXK     30
     33: static PetscErrorCode KSPGMRESUpdateHessenberg(KSP,PetscInt,PetscBool,PetscReal*);
     34: static PetscErrorCode KSPGMRESBuildSoln(PetscScalar*,Vec,Vec,KSP,PetscInt);

     36: PetscErrorCode    KSPSetUp_GMRES(KSP ksp)
     37: {
     38:   PetscInt       hh,hes,rs,cc;
     39:   PetscInt       max_k,k;
     40:   KSP_GMRES      *gmres = (KSP_GMRES*)ksp->data;

     42:   max_k = gmres->max_k;          /* restart size */
     43:   hh    = (max_k + 2) * (max_k + 1);
     44:   hes   = (max_k + 1) * (max_k + 1);
     45:   rs    = (max_k + 2);
     46:   cc    = (max_k + 1);

     48:   PetscCalloc5(hh,&gmres->hh_origin,hes,&gmres->hes_origin,rs,&gmres->rs_origin,cc,&gmres->cc_origin,cc,&gmres->ss_origin);
     49:   PetscLogObjectMemory((PetscObject)ksp,(hh + hes + rs + 2*cc)*sizeof(PetscScalar));

     51:   if (ksp->calc_sings) {
     52:     /* Allocate workspace to hold Hessenberg matrix needed by lapack */
     53:     PetscMalloc1((max_k + 3)*(max_k + 9),&gmres->Rsvd);
     54:     PetscLogObjectMemory((PetscObject)ksp,(max_k + 3)*(max_k + 9)*sizeof(PetscScalar));
     55:     PetscMalloc1(6*(max_k+2),&gmres->Dsvd);
     56:     PetscLogObjectMemory((PetscObject)ksp,6*(max_k+2)*sizeof(PetscReal));
     57:   }

     59:   /* Allocate array to hold pointers to user vectors.  Note that we need
     60:    4 + max_k + 1 (since we need it+1 vectors, and it <= max_k) */
     61:   gmres->vecs_allocated = VEC_OFFSET + 2 + max_k + gmres->nextra_vecs;

     63:   PetscMalloc1(gmres->vecs_allocated,&gmres->vecs);
     64:   PetscMalloc1(VEC_OFFSET+2+max_k,&gmres->user_work);
     65:   PetscMalloc1(VEC_OFFSET+2+max_k,&gmres->mwork_alloc);
     66:   PetscLogObjectMemory((PetscObject)ksp,(VEC_OFFSET+2+max_k)*(sizeof(Vec*)+sizeof(PetscInt)) + gmres->vecs_allocated*sizeof(Vec));

     68:   if (gmres->q_preallocate) {
     69:     gmres->vv_allocated = VEC_OFFSET + 2 + max_k;

     71:     KSPCreateVecs(ksp,gmres->vv_allocated,&gmres->user_work[0],0,NULL);
     72:     PetscLogObjectParents(ksp,gmres->vv_allocated,gmres->user_work[0]);

     74:     gmres->mwork_alloc[0] = gmres->vv_allocated;
     75:     gmres->nwork_alloc    = 1;
     76:     for (k=0; k<gmres->vv_allocated; k++) {
     77:       gmres->vecs[k] = gmres->user_work[0][k];
     78:     }
     79:   } else {
     80:     gmres->vv_allocated = 5;

     82:     KSPCreateVecs(ksp,5,&gmres->user_work[0],0,NULL);
     83:     PetscLogObjectParents(ksp,5,gmres->user_work[0]);

     85:     gmres->mwork_alloc[0] = 5;
     86:     gmres->nwork_alloc    = 1;
     87:     for (k=0; k<gmres->vv_allocated; k++) {
     88:       gmres->vecs[k] = gmres->user_work[0][k];
     89:     }
     90:   }
     91:   return 0;
     92: }

     94: /*
     95:     Run gmres, possibly with restart.  Return residual history if requested.
     96:     input parameters:

     98: .        gmres  - structure containing parameters and work areas

    100:     output parameters:
    101: .        nres    - residuals (from preconditioned system) at each step.
    102:                   If restarting, consider passing nres+it.  If null,
    103:                   ignored
    104: .        itcount - number of iterations used.  nres[0] to nres[itcount]
    105:                   are defined.  If null, ignored.

    107:     Notes:
    108:     On entry, the value in vector VEC_VV(0) should be the initial residual
    109:     (this allows shortcuts where the initial preconditioned residual is 0).
    110:  */
    111: PetscErrorCode KSPGMRESCycle(PetscInt *itcount,KSP ksp)
    112: {
    113:   KSP_GMRES      *gmres = (KSP_GMRES*)(ksp->data);
    114:   PetscReal      res,hapbnd,tt;
    115:   PetscInt       it     = 0, max_k = gmres->max_k;
    116:   PetscBool      hapend = PETSC_FALSE;

    118:   if (itcount) *itcount = 0;
    119:   VecNormalize(VEC_VV(0),&res);
    120:   KSPCheckNorm(ksp,res);

    122:   /* the constant .1 is arbitrary, just some measure at how incorrect the residuals are */
    123:   if ((ksp->rnorm > 0.0) && (PetscAbsReal(res-ksp->rnorm) > gmres->breakdowntol*gmres->rnorm0)) {
    125:     else {
    126:       PetscInfo(ksp,"Residual norm computed by GMRES recursion formula %g is far from the computed residual norm %g at restart, residual norm at start of cycle %g",(double)ksp->rnorm,(double)res,(double)gmres->rnorm0);
    127:       ksp->reason =  KSP_DIVERGED_BREAKDOWN;
    128:       return 0;
    129:     }
    130:   }
    131:   *GRS(0) = gmres->rnorm0 = res;

    133:   /* check for the convergence */
    134:   PetscObjectSAWsTakeAccess((PetscObject)ksp);
    135:   ksp->rnorm = res;
    136:   PetscObjectSAWsGrantAccess((PetscObject)ksp);
    137:   gmres->it  = (it - 1);
    138:   KSPLogResidualHistory(ksp,res);
    139:   KSPLogErrorHistory(ksp);
    140:   KSPMonitor(ksp,ksp->its,res);
    141:   if (!res) {
    142:     ksp->reason = KSP_CONVERGED_ATOL;
    143:     PetscInfo(ksp,"Converged due to zero residual norm on entry\n");
    144:     return 0;
    145:   }

    147:   (*ksp->converged)(ksp,ksp->its,res,&ksp->reason,ksp->cnvP);
    148:   while (!ksp->reason && it < max_k && ksp->its < ksp->max_it) {
    149:     if (it) {
    150:       KSPLogResidualHistory(ksp,res);
    151:       KSPLogErrorHistory(ksp);
    152:       KSPMonitor(ksp,ksp->its,res);
    153:     }
    154:     gmres->it = (it - 1);
    155:     if (gmres->vv_allocated <= it + VEC_OFFSET + 1) {
    156:       KSPGMRESGetNewVectors(ksp,it+1);
    157:     }
    158:     KSP_PCApplyBAorAB(ksp,VEC_VV(it),VEC_VV(1+it),VEC_TEMP_MATOP);

    160:     /* update hessenberg matrix and do Gram-Schmidt */
    161:     (*gmres->orthog)(ksp,it);
    162:     if (ksp->reason) break;

    164:     /* vv(i+1) . vv(i+1) */
    165:     VecNormalize(VEC_VV(it+1),&tt);
    166:     KSPCheckNorm(ksp,tt);

    168:     /* save the magnitude */
    169:     *HH(it+1,it)  = tt;
    170:     *HES(it+1,it) = tt;

    172:     /* check for the happy breakdown */
    173:     hapbnd = PetscAbsScalar(tt / *GRS(it));
    174:     if (hapbnd > gmres->haptol) hapbnd = gmres->haptol;
    175:     if (tt < hapbnd) {
    176:       PetscInfo(ksp,"Detected happy breakdown, current hapbnd = %14.12e tt = %14.12e\n",(double)hapbnd,(double)tt);
    177:       hapend = PETSC_TRUE;
    178:     }
    179:     KSPGMRESUpdateHessenberg(ksp,it,hapend,&res);

    181:     it++;
    182:     gmres->it = (it-1);   /* For converged */
    183:     ksp->its++;
    184:     ksp->rnorm = res;
    185:     if (ksp->reason) break;

    187:     (*ksp->converged)(ksp,ksp->its,res,&ksp->reason,ksp->cnvP);

    189:     /* Catch error in happy breakdown and signal convergence and break from loop */
    190:     if (hapend) {
    191:       if (ksp->normtype == KSP_NORM_NONE) { /* convergence test was skipped in this case */
    192:         ksp->reason = KSP_CONVERGED_HAPPY_BREAKDOWN;
    193:       } else if (!ksp->reason) {
    195:         else {
    196:           ksp->reason = KSP_DIVERGED_BREAKDOWN;
    197:           break;
    198:         }
    199:       }
    200:     }
    201:   }

    203:   /* Monitor if we know that we will not return for a restart */
    204:   if (it && (ksp->reason || ksp->its >= ksp->max_it)) {
    205:     KSPLogResidualHistory(ksp,res);
    206:     KSPLogErrorHistory(ksp);
    207:     KSPMonitor(ksp,ksp->its,res);
    208:   }

    210:   if (itcount) *itcount = it;

    212:   /*
    213:     Down here we have to solve for the "best" coefficients of the Krylov
    214:     columns, add the solution values together, and possibly unwind the
    215:     preconditioning from the solution
    216:    */
    217:   /* Form the solution (or the solution so far) */
    218:   KSPGMRESBuildSoln(GRS(0),ksp->vec_sol,ksp->vec_sol,ksp,it-1);
    219:   return 0;
    220: }

    222: PetscErrorCode KSPSolve_GMRES(KSP ksp)
    223: {
    224:   PetscInt       its,itcount,i;
    225:   KSP_GMRES      *gmres     = (KSP_GMRES*)ksp->data;
    226:   PetscBool      guess_zero = ksp->guess_zero;
    227:   PetscInt       N = gmres->max_k + 1;

    231:   PetscObjectSAWsTakeAccess((PetscObject)ksp);
    232:   ksp->its = 0;
    233:   PetscObjectSAWsGrantAccess((PetscObject)ksp);

    235:   itcount     = 0;
    236:   gmres->fullcycle = 0;
    237:   ksp->rnorm  = -1.0; /* special marker for KSPGMRESCycle() */
    238:   while (!ksp->reason || (ksp->rnorm == -1 && ksp->reason == KSP_DIVERGED_PC_FAILED)) {
    239:     KSPInitialResidual(ksp,ksp->vec_sol,VEC_TEMP,VEC_TEMP_MATOP,VEC_VV(0),ksp->vec_rhs);
    240:     KSPGMRESCycle(&its,ksp);
    241:     /* Store the Hessenberg matrix and the basis vectors of the Krylov subspace
    242:     if the cycle is complete for the computation of the Ritz pairs */
    243:     if (its == gmres->max_k) {
    244:       gmres->fullcycle++;
    245:       if (ksp->calc_ritz) {
    246:         if (!gmres->hes_ritz) {
    247:           PetscMalloc1(N*N,&gmres->hes_ritz);
    248:           PetscLogObjectMemory((PetscObject)ksp,N*N*sizeof(PetscScalar));
    249:           VecDuplicateVecs(VEC_VV(0),N,&gmres->vecb);
    250:         }
    251:         PetscArraycpy(gmres->hes_ritz,gmres->hes_origin,N*N);
    252:         for (i=0; i<gmres->max_k+1; i++) {
    253:           VecCopy(VEC_VV(i),gmres->vecb[i]);
    254:         }
    255:       }
    256:     }
    257:     itcount += its;
    258:     if (itcount >= ksp->max_it) {
    259:       if (!ksp->reason) ksp->reason = KSP_DIVERGED_ITS;
    260:       break;
    261:     }
    262:     ksp->guess_zero = PETSC_FALSE; /* every future call to KSPInitialResidual() will have nonzero guess */
    263:   }
    264:   ksp->guess_zero = guess_zero; /* restore if user provided nonzero initial guess */
    265:   return 0;
    266: }

    268: PetscErrorCode KSPReset_GMRES(KSP ksp)
    269: {
    270:   KSP_GMRES      *gmres = (KSP_GMRES*)ksp->data;
    271:   PetscInt       i;

    273:   /* Free the Hessenberg matrices */
    274:   PetscFree5(gmres->hh_origin,gmres->hes_origin,gmres->rs_origin,gmres->cc_origin,gmres->ss_origin);
    275:   PetscFree(gmres->hes_ritz);

    277:   /* free work vectors */
    278:   PetscFree(gmres->vecs);
    279:   for (i=0; i<gmres->nwork_alloc; i++) {
    280:     VecDestroyVecs(gmres->mwork_alloc[i],&gmres->user_work[i]);
    281:   }
    282:   gmres->nwork_alloc = 0;
    283:   if (gmres->vecb)  {
    284:     VecDestroyVecs(gmres->max_k+1,&gmres->vecb);
    285:   }

    287:   PetscFree(gmres->user_work);
    288:   PetscFree(gmres->mwork_alloc);
    289:   PetscFree(gmres->nrs);
    290:   VecDestroy(&gmres->sol_temp);
    291:   PetscFree(gmres->Rsvd);
    292:   PetscFree(gmres->Dsvd);
    293:   PetscFree(gmres->orthogwork);

    295:   gmres->vv_allocated   = 0;
    296:   gmres->vecs_allocated = 0;
    297:   gmres->sol_temp       = NULL;
    298:   return 0;
    299: }

    301: PetscErrorCode KSPDestroy_GMRES(KSP ksp)
    302: {
    303:   KSPReset_GMRES(ksp);
    304:   PetscFree(ksp->data);
    305:   /* clear composed functions */
    306:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetPreAllocateVectors_C",NULL);
    307:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetOrthogonalization_C",NULL);
    308:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetOrthogonalization_C",NULL);
    309:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetRestart_C",NULL);
    310:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetRestart_C",NULL);
    311:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetHapTol_C",NULL);
    312:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetBreakdownTolerance_C",NULL);
    313:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetCGSRefinementType_C",NULL);
    314:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetCGSRefinementType_C",NULL);
    315:   return 0;
    316: }
    317: /*
    318:     KSPGMRESBuildSoln - create the solution from the starting vector and the
    319:     current iterates.

    321:     Input parameters:
    322:         nrs - work area of size it + 1.
    323:         vs  - index of initial guess
    324:         vdest - index of result.  Note that vs may == vdest (replace
    325:                 guess with the solution).

    327:      This is an internal routine that knows about the GMRES internals.
    328:  */
    329: static PetscErrorCode KSPGMRESBuildSoln(PetscScalar *nrs,Vec vs,Vec vdest,KSP ksp,PetscInt it)
    330: {
    331:   PetscScalar    tt;
    332:   PetscInt       ii,k,j;
    333:   KSP_GMRES      *gmres = (KSP_GMRES*)(ksp->data);

    335:   /* Solve for solution vector that minimizes the residual */

    337:   /* If it is < 0, no gmres steps have been performed */
    338:   if (it < 0) {
    339:     VecCopy(vs,vdest); /* VecCopy() is smart, exists immediately if vguess == vdest */
    340:     return 0;
    341:   }
    342:   if (*HH(it,it) != 0.0) {
    343:     nrs[it] = *GRS(it) / *HH(it,it);
    344:   } else {
    346:     else ksp->reason = KSP_DIVERGED_BREAKDOWN;

    348:     PetscInfo(ksp,"Likely your matrix or preconditioner is singular. HH(it,it) is identically zero; it = %D GRS(it) = %g\n",it,(double)PetscAbsScalar(*GRS(it)));
    349:     return 0;
    350:   }
    351:   for (ii=1; ii<=it; ii++) {
    352:     k  = it - ii;
    353:     tt = *GRS(k);
    354:     for (j=k+1; j<=it; j++) tt = tt - *HH(k,j) * nrs[j];
    355:     if (*HH(k,k) == 0.0) {
    357:       else {
    358:         ksp->reason = KSP_DIVERGED_BREAKDOWN;
    359:         PetscInfo(ksp,"Likely your matrix or preconditioner is singular. HH(k,k) is identically zero; k = %D\n",k);
    360:         return 0;
    361:       }
    362:     }
    363:     nrs[k] = tt / *HH(k,k);
    364:   }

    366:   /* Accumulate the correction to the solution of the preconditioned problem in TEMP */
    367:   VecSet(VEC_TEMP,0.0);
    368:   VecMAXPY(VEC_TEMP,it+1,nrs,&VEC_VV(0));

    370:   KSPUnwindPreconditioner(ksp,VEC_TEMP,VEC_TEMP_MATOP);
    371:   /* add solution to previous solution */
    372:   if (vdest != vs) {
    373:     VecCopy(vs,vdest);
    374:   }
    375:   VecAXPY(vdest,1.0,VEC_TEMP);
    376:   return 0;
    377: }
    378: /*
    379:    Do the scalar work for the orthogonalization.  Return new residual norm.
    380:  */
    381: static PetscErrorCode KSPGMRESUpdateHessenberg(KSP ksp,PetscInt it,PetscBool hapend,PetscReal *res)
    382: {
    383:   PetscScalar *hh,*cc,*ss,tt;
    384:   PetscInt    j;
    385:   KSP_GMRES   *gmres = (KSP_GMRES*)(ksp->data);

    387:   hh = HH(0,it);
    388:   cc = CC(0);
    389:   ss = SS(0);

    391:   /* Apply all the previously computed plane rotations to the new column
    392:      of the Hessenberg matrix */
    393:   for (j=1; j<=it; j++) {
    394:     tt  = *hh;
    395:     *hh = PetscConj(*cc) * tt + *ss * *(hh+1);
    396:     hh++;
    397:     *hh = *cc++ * *hh - (*ss++ * tt);
    398:   }

    400:   /*
    401:     compute the new plane rotation, and apply it to:
    402:      1) the right-hand-side of the Hessenberg system
    403:      2) the new column of the Hessenberg matrix
    404:     thus obtaining the updated value of the residual
    405:   */
    406:   if (!hapend) {
    407:     tt = PetscSqrtScalar(PetscConj(*hh) * *hh + PetscConj(*(hh+1)) * *(hh+1));
    408:     if (tt == 0.0) {
    410:       else {
    411:         ksp->reason = KSP_DIVERGED_NULL;
    412:         return 0;
    413:       }
    414:     }
    415:     *cc        = *hh / tt;
    416:     *ss        = *(hh+1) / tt;
    417:     *GRS(it+1) = -(*ss * *GRS(it));
    418:     *GRS(it)   = PetscConj(*cc) * *GRS(it);
    419:     *hh        = PetscConj(*cc) * *hh + *ss * *(hh+1);
    420:     *res       = PetscAbsScalar(*GRS(it+1));
    421:   } else {
    422:     /* happy breakdown: HH(it+1, it) = 0, therefore we don't need to apply
    423:             another rotation matrix (so RH doesn't change).  The new residual is
    424:             always the new sine term times the residual from last time (GRS(it)),
    425:             but now the new sine rotation would be zero...so the residual should
    426:             be zero...so we will multiply "zero" by the last residual.  This might
    427:             not be exactly what we want to do here -could just return "zero". */

    429:     *res = 0.0;
    430:   }
    431:   return 0;
    432: }
    433: /*
    434:    This routine allocates more work vectors, starting from VEC_VV(it).
    435:  */
    436: PetscErrorCode KSPGMRESGetNewVectors(KSP ksp,PetscInt it)
    437: {
    438:   KSP_GMRES      *gmres = (KSP_GMRES*)ksp->data;
    439:   PetscInt       nwork = gmres->nwork_alloc,k,nalloc;

    441:   nalloc = PetscMin(ksp->max_it,gmres->delta_allocate);
    442:   /* Adjust the number to allocate to make sure that we don't exceed the
    443:     number of available slots */
    444:   if (it + VEC_OFFSET + nalloc >= gmres->vecs_allocated) {
    445:     nalloc = gmres->vecs_allocated - it - VEC_OFFSET;
    446:   }
    447:   if (!nalloc) return 0;

    449:   gmres->vv_allocated += nalloc;

    451:   KSPCreateVecs(ksp,nalloc,&gmres->user_work[nwork],0,NULL);
    452:   PetscLogObjectParents(ksp,nalloc,gmres->user_work[nwork]);

    454:   gmres->mwork_alloc[nwork] = nalloc;
    455:   for (k=0; k<nalloc; k++) {
    456:     gmres->vecs[it+VEC_OFFSET+k] = gmres->user_work[nwork][k];
    457:   }
    458:   gmres->nwork_alloc++;
    459:   return 0;
    460: }

    462: PetscErrorCode KSPBuildSolution_GMRES(KSP ksp,Vec ptr,Vec *result)
    463: {
    464:   KSP_GMRES      *gmres = (KSP_GMRES*)ksp->data;

    466:   if (!ptr) {
    467:     if (!gmres->sol_temp) {
    468:       VecDuplicate(ksp->vec_sol,&gmres->sol_temp);
    469:       PetscLogObjectParent((PetscObject)ksp,(PetscObject)gmres->sol_temp);
    470:     }
    471:     ptr = gmres->sol_temp;
    472:   }
    473:   if (!gmres->nrs) {
    474:     /* allocate the work area */
    475:     PetscMalloc1(gmres->max_k,&gmres->nrs);
    476:     PetscLogObjectMemory((PetscObject)ksp,gmres->max_k);
    477:   }

    479:   KSPGMRESBuildSoln(gmres->nrs,ksp->vec_sol,ptr,ksp,gmres->it);
    480:   if (result) *result = ptr;
    481:   return 0;
    482: }

    484: PetscErrorCode KSPView_GMRES(KSP ksp,PetscViewer viewer)
    485: {
    486:   KSP_GMRES      *gmres = (KSP_GMRES*)ksp->data;
    487:   const char     *cstr;
    488:   PetscBool      iascii,isstring;

    490:   PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&iascii);
    491:   PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERSTRING,&isstring);
    492:   if (gmres->orthog == KSPGMRESClassicalGramSchmidtOrthogonalization) {
    493:     switch (gmres->cgstype) {
    494:     case (KSP_GMRES_CGS_REFINE_NEVER):
    495:       cstr = "Classical (unmodified) Gram-Schmidt Orthogonalization with no iterative refinement";
    496:       break;
    497:     case (KSP_GMRES_CGS_REFINE_ALWAYS):
    498:       cstr = "Classical (unmodified) Gram-Schmidt Orthogonalization with one step of iterative refinement";
    499:       break;
    500:     case (KSP_GMRES_CGS_REFINE_IFNEEDED):
    501:       cstr = "Classical (unmodified) Gram-Schmidt Orthogonalization with one step of iterative refinement when needed";
    502:       break;
    503:     default:
    504:       SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_ARG_OUTOFRANGE,"Unknown orthogonalization");
    505:     }
    506:   } else if (gmres->orthog == KSPGMRESModifiedGramSchmidtOrthogonalization) {
    507:     cstr = "Modified Gram-Schmidt Orthogonalization";
    508:   } else {
    509:     cstr = "unknown orthogonalization";
    510:   }
    511:   if (iascii) {
    512:     PetscViewerASCIIPrintf(viewer,"  restart=%D, using %s\n",gmres->max_k,cstr);
    513:     PetscViewerASCIIPrintf(viewer,"  happy breakdown tolerance %g\n",(double)gmres->haptol);
    514:   } else if (isstring) {
    515:     PetscViewerStringSPrintf(viewer,"%s restart %D",cstr,gmres->max_k);
    516:   }
    517:   return 0;
    518: }

    520: /*@C
    521:    KSPGMRESMonitorKrylov - Calls VecView() for each new direction in the GMRES accumulated Krylov space.

    523:    Collective on ksp

    525:    Input Parameters:
    526: +  ksp - the KSP context
    527: .  its - iteration number
    528: .  fgnorm - 2-norm of residual (or gradient)
    529: -  dummy - an collection of viewers created with KSPViewerCreate()

    531:    Options Database Keys:
    532: .   -ksp_gmres_krylov_monitor <bool> - Plot the Krylov directions

    534:    Notes:
    535:     A new PETSCVIEWERDRAW is created for each Krylov vector so they can all be simultaneously viewed
    536:    Level: intermediate

    538: .seealso: KSPMonitorSet(), KSPMonitorResidual(), VecView(), KSPViewersCreate(), KSPViewersDestroy()
    539: @*/
    540: PetscErrorCode  KSPGMRESMonitorKrylov(KSP ksp,PetscInt its,PetscReal fgnorm,void *dummy)
    541: {
    542:   PetscViewers   viewers = (PetscViewers)dummy;
    543:   KSP_GMRES      *gmres  = (KSP_GMRES*)ksp->data;
    544:   Vec            x;
    545:   PetscViewer    viewer;
    546:   PetscBool      flg;

    548:   PetscViewersGetViewer(viewers,gmres->it+1,&viewer);
    549:   PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERDRAW,&flg);
    550:   if (!flg) {
    551:     PetscViewerSetType(viewer,PETSCVIEWERDRAW);
    552:     PetscViewerDrawSetInfo(viewer,NULL,"Krylov GMRES Monitor",PETSC_DECIDE,PETSC_DECIDE,300,300);
    553:   }
    554:   x    = VEC_VV(gmres->it+1);
    555:   VecView(x,viewer);
    556:   return 0;
    557: }

    559: PetscErrorCode KSPSetFromOptions_GMRES(PetscOptionItems *PetscOptionsObject,KSP ksp)
    560: {
    562:   PetscInt       restart;
    563:   PetscReal      haptol,breakdowntol;
    564:   KSP_GMRES      *gmres = (KSP_GMRES*)ksp->data;
    565:   PetscBool      flg;

    567:   PetscOptionsHead(PetscOptionsObject,"KSP GMRES Options");
    568:   PetscOptionsInt("-ksp_gmres_restart","Number of Krylov search directions","KSPGMRESSetRestart",gmres->max_k,&restart,&flg);
    569:   if (flg) KSPGMRESSetRestart(ksp,restart);
    570:   PetscOptionsReal("-ksp_gmres_haptol","Tolerance for exact convergence (happy ending)","KSPGMRESSetHapTol",gmres->haptol,&haptol,&flg);
    571:   if (flg) KSPGMRESSetHapTol(ksp,haptol);
    572:   PetscOptionsReal("-ksp_gmres_breakdown_tolerance","Divergence breakdown tolerance during GMRES restart","KSPGMRESSetBreakdownTolerance",gmres->breakdowntol,&breakdowntol,&flg);
    573:   if (flg) KSPGMRESSetBreakdownTolerance(ksp,breakdowntol);
    574:   flg  = PETSC_FALSE;
    575:   PetscOptionsBool("-ksp_gmres_preallocate","Preallocate Krylov vectors","KSPGMRESSetPreAllocateVectors",flg,&flg,NULL);
    576:   if (flg) KSPGMRESSetPreAllocateVectors(ksp);
    577:   PetscOptionsBoolGroupBegin("-ksp_gmres_classicalgramschmidt","Classical (unmodified) Gram-Schmidt (fast)","KSPGMRESSetOrthogonalization",&flg);
    578:   if (flg) KSPGMRESSetOrthogonalization(ksp,KSPGMRESClassicalGramSchmidtOrthogonalization);
    579:   PetscOptionsBoolGroupEnd("-ksp_gmres_modifiedgramschmidt","Modified Gram-Schmidt (slow,more stable)","KSPGMRESSetOrthogonalization",&flg);
    580:   if (flg) KSPGMRESSetOrthogonalization(ksp,KSPGMRESModifiedGramSchmidtOrthogonalization);
    581:   PetscOptionsEnum("-ksp_gmres_cgs_refinement_type","Type of iterative refinement for classical (unmodified) Gram-Schmidt","KSPGMRESSetCGSRefinementType",
    582:                           KSPGMRESCGSRefinementTypes,(PetscEnum)gmres->cgstype,(PetscEnum*)&gmres->cgstype,&flg);
    583:   flg  = PETSC_FALSE;
    584:   PetscOptionsBool("-ksp_gmres_krylov_monitor","Plot the Krylov directions","KSPMonitorSet",flg,&flg,NULL);
    585:   if (flg) {
    586:     PetscViewers viewers;
    587:     PetscViewersCreate(PetscObjectComm((PetscObject)ksp),&viewers);
    588:     KSPMonitorSet(ksp,KSPGMRESMonitorKrylov,viewers,(PetscErrorCode (*)(void**))PetscViewersDestroy);
    589:   }
    590:   PetscOptionsTail();
    591:   return 0;
    592: }

    594: PetscErrorCode  KSPGMRESSetHapTol_GMRES(KSP ksp,PetscReal tol)
    595: {
    596:   KSP_GMRES *gmres = (KSP_GMRES*)ksp->data;

    599:   gmres->haptol = tol;
    600:   return 0;
    601: }

    603: PetscErrorCode  KSPGMRESSetBreakdownTolerance_GMRES(KSP ksp,PetscReal tol)
    604: {
    605:   KSP_GMRES *gmres = (KSP_GMRES*)ksp->data;

    607:   if (tol == PETSC_DEFAULT) {
    608:     gmres->breakdowntol = 0.1;
    609:     return 0;
    610:   }
    612:   gmres->breakdowntol = tol;
    613:   return 0;
    614: }

    616: PetscErrorCode  KSPGMRESGetRestart_GMRES(KSP ksp,PetscInt *max_k)
    617: {
    618:   KSP_GMRES *gmres = (KSP_GMRES*)ksp->data;

    620:   *max_k = gmres->max_k;
    621:   return 0;
    622: }

    624: PetscErrorCode  KSPGMRESSetRestart_GMRES(KSP ksp,PetscInt max_k)
    625: {
    626:   KSP_GMRES      *gmres = (KSP_GMRES*)ksp->data;

    629:   if (!ksp->setupstage) {
    630:     gmres->max_k = max_k;
    631:   } else if (gmres->max_k != max_k) {
    632:     gmres->max_k    = max_k;
    633:     ksp->setupstage = KSP_SETUP_NEW;
    634:     /* free the data structures, then create them again */
    635:     KSPReset_GMRES(ksp);
    636:   }
    637:   return 0;
    638: }

    640: PetscErrorCode  KSPGMRESSetOrthogonalization_GMRES(KSP ksp,FCN fcn)
    641: {
    642:   ((KSP_GMRES*)ksp->data)->orthog = fcn;
    643:   return 0;
    644: }

    646: PetscErrorCode  KSPGMRESGetOrthogonalization_GMRES(KSP ksp,FCN *fcn)
    647: {
    648:   *fcn = ((KSP_GMRES*)ksp->data)->orthog;
    649:   return 0;
    650: }

    652: PetscErrorCode  KSPGMRESSetPreAllocateVectors_GMRES(KSP ksp)
    653: {
    654:   KSP_GMRES *gmres;

    656:   gmres = (KSP_GMRES*)ksp->data;
    657:   gmres->q_preallocate = 1;
    658:   return 0;
    659: }

    661: PetscErrorCode  KSPGMRESSetCGSRefinementType_GMRES(KSP ksp,KSPGMRESCGSRefinementType type)
    662: {
    663:   KSP_GMRES *gmres = (KSP_GMRES*)ksp->data;

    665:   gmres->cgstype = type;
    666:   return 0;
    667: }

    669: PetscErrorCode  KSPGMRESGetCGSRefinementType_GMRES(KSP ksp,KSPGMRESCGSRefinementType *type)
    670: {
    671:   KSP_GMRES *gmres = (KSP_GMRES*)ksp->data;

    673:   *type = gmres->cgstype;
    674:   return 0;
    675: }

    677: /*@
    678:    KSPGMRESSetCGSRefinementType - Sets the type of iterative refinement to use
    679:          in the classical Gram Schmidt orthogonalization.

    681:    Logically Collective on ksp

    683:    Input Parameters:
    684: +  ksp - the Krylov space context
    685: -  type - the type of refinement

    687:   Options Database:
    688: .  -ksp_gmres_cgs_refinement_type <refine_never,refine_ifneeded,refine_always> - refinement type

    690:    Level: intermediate

    692: .seealso: KSPGMRESSetOrthogonalization(), KSPGMRESCGSRefinementType, KSPGMRESClassicalGramSchmidtOrthogonalization(), KSPGMRESGetCGSRefinementType(),
    693:           KSPGMRESGetOrthogonalization()
    694: @*/
    695: PetscErrorCode  KSPGMRESSetCGSRefinementType(KSP ksp,KSPGMRESCGSRefinementType type)
    696: {
    699:   PetscTryMethod(ksp,"KSPGMRESSetCGSRefinementType_C",(KSP,KSPGMRESCGSRefinementType),(ksp,type));
    700:   return 0;
    701: }

    703: /*@
    704:    KSPGMRESGetCGSRefinementType - Gets the type of iterative refinement to use
    705:          in the classical Gram Schmidt orthogonalization.

    707:    Not Collective

    709:    Input Parameter:
    710: .  ksp - the Krylov space context

    712:    Output Parameter:
    713: .  type - the type of refinement

    715:   Options Database:
    716: .  -ksp_gmres_cgs_refinement_type <refine_never,refine_ifneeded,refine_always> - type of refinement

    718:    Level: intermediate

    720: .seealso: KSPGMRESSetOrthogonalization(), KSPGMRESCGSRefinementType, KSPGMRESClassicalGramSchmidtOrthogonalization(), KSPGMRESSetCGSRefinementType(),
    721:           KSPGMRESGetOrthogonalization()
    722: @*/
    723: PetscErrorCode  KSPGMRESGetCGSRefinementType(KSP ksp,KSPGMRESCGSRefinementType *type)
    724: {
    726:   PetscUseMethod(ksp,"KSPGMRESGetCGSRefinementType_C",(KSP,KSPGMRESCGSRefinementType*),(ksp,type));
    727:   return 0;
    728: }

    730: /*@
    731:    KSPGMRESSetRestart - Sets number of iterations at which GMRES, FGMRES and LGMRES restarts.

    733:    Logically Collective on ksp

    735:    Input Parameters:
    736: +  ksp - the Krylov space context
    737: -  restart - integer restart value

    739:   Options Database:
    740: .  -ksp_gmres_restart <positive integer> - integer restart value

    742:     Note: The default value is 30.

    744:    Level: intermediate

    746: .seealso: KSPSetTolerances(), KSPGMRESSetOrthogonalization(), KSPGMRESSetPreAllocateVectors(), KSPGMRESGetRestart()
    747: @*/
    748: PetscErrorCode  KSPGMRESSetRestart(KSP ksp, PetscInt restart)
    749: {

    752:   PetscTryMethod(ksp,"KSPGMRESSetRestart_C",(KSP,PetscInt),(ksp,restart));
    753:   return 0;
    754: }

    756: /*@
    757:    KSPGMRESGetRestart - Gets number of iterations at which GMRES, FGMRES and LGMRES restarts.

    759:    Not Collective

    761:    Input Parameter:
    762: .  ksp - the Krylov space context

    764:    Output Parameter:
    765: .   restart - integer restart value

    767:     Note: The default value is 30.

    769:    Level: intermediate

    771: .seealso: KSPSetTolerances(), KSPGMRESSetOrthogonalization(), KSPGMRESSetPreAllocateVectors(), KSPGMRESSetRestart()
    772: @*/
    773: PetscErrorCode  KSPGMRESGetRestart(KSP ksp, PetscInt *restart)
    774: {
    775:   PetscUseMethod(ksp,"KSPGMRESGetRestart_C",(KSP,PetscInt*),(ksp,restart));
    776:   return 0;
    777: }

    779: /*@
    780:    KSPGMRESSetHapTol - Sets tolerance for determining happy breakdown in GMRES, FGMRES and LGMRES.

    782:    Logically Collective on ksp

    784:    Input Parameters:
    785: +  ksp - the Krylov space context
    786: -  tol - the tolerance

    788:   Options Database:
    789: .  -ksp_gmres_haptol <positive real value> - set tolerance for determining happy breakdown

    791:    Note: Happy breakdown is the rare case in GMRES where an 'exact' solution is obtained after
    792:          a certain number of iterations. If you attempt more iterations after this point unstable
    793:          things can happen hence very occasionally you may need to set this value to detect this condition

    795:    Level: intermediate

    797: .seealso: KSPSetTolerances()
    798: @*/
    799: PetscErrorCode  KSPGMRESSetHapTol(KSP ksp,PetscReal tol)
    800: {
    802:   PetscTryMethod((ksp),"KSPGMRESSetHapTol_C",(KSP,PetscReal),((ksp),(tol)));
    803:   return 0;
    804: }

    806: /*@
    807:    KSPGMRESSetBreakdownTolerance - Sets tolerance for determining divergence breakdown in GMRES.

    809:    Logically Collective on ksp

    811:    Input Parameters:
    812: +  ksp - the Krylov space context
    813: -  tol - the tolerance

    815:   Options Database:
    816: .  -ksp_gmres_breakdown_tolerance <positive real value> - set tolerance for determining divergence breakdown

    818:    Note: divergence breakdown occurs when GMRES residual increases significantly
    819:          during restart

    821:    Level: intermediate

    823: .seealso: KSPSetTolerances(), KSPGMRESSetHapTol()
    824: @*/
    825: PetscErrorCode  KSPGMRESSetBreakdownTolerance(KSP ksp,PetscReal tol)
    826: {
    828:   PetscTryMethod((ksp),"KSPGMRESSetBreakdownTolerance_C",(KSP,PetscReal),(ksp,tol));
    829:   return 0;
    830: }

    832: /*MC
    833:      KSPGMRES - Implements the Generalized Minimal Residual method.
    834:                 (Saad and Schultz, 1986) with restart

    836:    Options Database Keys:
    837: +   -ksp_gmres_restart <restart> - the number of Krylov directions to orthogonalize against
    838: .   -ksp_gmres_haptol <tol> - sets the tolerance for "happy ending" (exact convergence)
    839: .   -ksp_gmres_preallocate - preallocate all the Krylov search directions initially (otherwise groups of
    840:                              vectors are allocated as needed)
    841: .   -ksp_gmres_classicalgramschmidt - use classical (unmodified) Gram-Schmidt to orthogonalize against the Krylov space (fast) (the default)
    842: .   -ksp_gmres_modifiedgramschmidt - use modified Gram-Schmidt in the orthogonalization (more stable, but slower)
    843: .   -ksp_gmres_cgs_refinement_type <refine_never,refine_ifneeded,refine_always> - determine if iterative refinement is used to increase the
    844:                                    stability of the classical Gram-Schmidt  orthogonalization.
    845: -   -ksp_gmres_krylov_monitor - plot the Krylov space generated

    847:    Level: beginner

    849:    Notes:
    850:     Left and right preconditioning are supported, but not symmetric preconditioning.

    852:    References:
    853: .  * - YOUCEF SAAD AND MARTIN H. SCHULTZ, GMRES: A GENERALIZED MINIMAL RESIDUAL ALGORITHM FOR SOLVING NONSYMMETRIC LINEAR SYSTEMS.
    854:           SIAM J. ScI. STAT. COMPUT. Vo|. 7, No. 3, July 1986.

    856: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPFGMRES, KSPLGMRES,
    857:            KSPGMRESSetRestart(), KSPGMRESSetHapTol(), KSPGMRESSetPreAllocateVectors(), KSPGMRESSetOrthogonalization(), KSPGMRESGetOrthogonalization(),
    858:            KSPGMRESClassicalGramSchmidtOrthogonalization(), KSPGMRESModifiedGramSchmidtOrthogonalization(),
    859:            KSPGMRESCGSRefinementType, KSPGMRESSetCGSRefinementType(), KSPGMRESGetCGSRefinementType(), KSPGMRESMonitorKrylov(), KSPSetPCSide()

    861: M*/

    863: PETSC_EXTERN PetscErrorCode KSPCreate_GMRES(KSP ksp)
    864: {
    865:   KSP_GMRES      *gmres;

    867:   PetscNewLog(ksp,&gmres);
    868:   ksp->data = (void*)gmres;

    870:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,4);
    871:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,3);
    872:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_SYMMETRIC,2);
    873:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_RIGHT,1);
    874:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,1);

    876:   ksp->ops->buildsolution                = KSPBuildSolution_GMRES;
    877:   ksp->ops->setup                        = KSPSetUp_GMRES;
    878:   ksp->ops->solve                        = KSPSolve_GMRES;
    879:   ksp->ops->reset                        = KSPReset_GMRES;
    880:   ksp->ops->destroy                      = KSPDestroy_GMRES;
    881:   ksp->ops->view                         = KSPView_GMRES;
    882:   ksp->ops->setfromoptions               = KSPSetFromOptions_GMRES;
    883:   ksp->ops->computeextremesingularvalues = KSPComputeExtremeSingularValues_GMRES;
    884:   ksp->ops->computeeigenvalues           = KSPComputeEigenvalues_GMRES;
    885: #if !defined(PETSC_USE_COMPLEX)
    886:   ksp->ops->computeritz                  = KSPComputeRitz_GMRES;
    887: #endif
    888:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetPreAllocateVectors_C",KSPGMRESSetPreAllocateVectors_GMRES);
    889:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetOrthogonalization_C",KSPGMRESSetOrthogonalization_GMRES);
    890:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetOrthogonalization_C",KSPGMRESGetOrthogonalization_GMRES);
    891:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetRestart_C",KSPGMRESSetRestart_GMRES);
    892:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetRestart_C",KSPGMRESGetRestart_GMRES);
    893:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetHapTol_C",KSPGMRESSetHapTol_GMRES);
    894:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetBreakdownTolerance_C",KSPGMRESSetBreakdownTolerance_GMRES);
    895:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetCGSRefinementType_C",KSPGMRESSetCGSRefinementType_GMRES);
    896:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetCGSRefinementType_C",KSPGMRESGetCGSRefinementType_GMRES);

    898:   gmres->haptol         = 1.0e-30;
    899:   gmres->breakdowntol   = 0.1;
    900:   gmres->q_preallocate  = 0;
    901:   gmres->delta_allocate = GMRES_DELTA_DIRECTIONS;
    902:   gmres->orthog         = KSPGMRESClassicalGramSchmidtOrthogonalization;
    903:   gmres->nrs            = NULL;
    904:   gmres->sol_temp       = NULL;
    905:   gmres->max_k          = GMRES_DEFAULT_MAXK;
    906:   gmres->Rsvd           = NULL;
    907:   gmres->cgstype        = KSP_GMRES_CGS_REFINE_NEVER;
    908:   gmres->orthogwork     = NULL;
    909:   return 0;
    910: }