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

Actual source code: fgmres.c

      2: /*
      3:     This file implements FGMRES (a Generalized Minimal Residual) method.
      4:     Reference:  Saad, 1993.

      6:     Preconditioning:  If the preconditioner is constant then this fgmres
      7:     code is equivalent to RIGHT-PRECONDITIONED GMRES.
      8:     FGMRES is a modification of gmres that allows the preconditioner to change
      9:     at each iteration.

     11:     Restarts:  Restarts are basically solves with x0 not equal to zero.

     13:        Contributed by Allison Baker

     15: */

     17: #include <../src/ksp/ksp/impls/gmres/fgmres/fgmresimpl.h>
     18: #define FGMRES_DELTA_DIRECTIONS 10
     19: #define FGMRES_DEFAULT_MAXK     30
     20: static PetscErrorCode KSPFGMRESGetNewVectors(KSP,PetscInt);
     21: static PetscErrorCode KSPFGMRESUpdateHessenberg(KSP,PetscInt,PetscBool,PetscReal*);
     22: static PetscErrorCode KSPFGMRESBuildSoln(PetscScalar*,Vec,Vec,KSP,PetscInt);

     24: /*

     26:     KSPSetUp_FGMRES - Sets up the workspace needed by fgmres.

     28:     This is called once, usually automatically by KSPSolve() or KSPSetUp(),
     29:     but can be called directly by KSPSetUp().

     31: */
     32: PetscErrorCode    KSPSetUp_FGMRES(KSP ksp)
     33: {
     34:   PetscInt       max_k,k;
     35:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)ksp->data;

     37:   max_k = fgmres->max_k;

     39:   KSPSetUp_GMRES(ksp);

     41:   PetscMalloc1(max_k+2,&fgmres->prevecs);
     42:   PetscMalloc1(max_k+2,&fgmres->prevecs_user_work);
     43:   PetscLogObjectMemory((PetscObject)ksp,(max_k+2)*(2*sizeof(void*)));

     45:   /* fgmres->vv_allocated includes extra work vectors, which are not used in the additional
     46:      block of vectors used to store the preconditioned directions, hence  the -VEC_OFFSET
     47:      term for this first allocation of vectors holding preconditioned directions */
     48:   KSPCreateVecs(ksp,fgmres->vv_allocated-VEC_OFFSET,&fgmres->prevecs_user_work[0],0,NULL);
     49:   PetscLogObjectParents(ksp,fgmres->vv_allocated-VEC_OFFSET,fgmres->prevecs_user_work[0]);
     50:   for (k=0; k < fgmres->vv_allocated - VEC_OFFSET ; k++) {
     51:     fgmres->prevecs[k] = fgmres->prevecs_user_work[0][k];
     52:   }
     53:   return 0;
     54: }

     56: /*
     57:     KSPFGMRESResidual - This routine computes the initial residual (NOT PRECONDITIONED)
     58: */
     59: static PetscErrorCode KSPFGMRESResidual(KSP ksp)
     60: {
     61:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)(ksp->data);
     62:   Mat            Amat,Pmat;

     64:   PCGetOperators(ksp->pc,&Amat,&Pmat);

     66:   /* put A*x into VEC_TEMP */
     67:   KSP_MatMult(ksp,Amat,ksp->vec_sol,VEC_TEMP);
     68:   /* now put residual (-A*x + f) into vec_vv(0) */
     69:   VecWAXPY(VEC_VV(0),-1.0,VEC_TEMP,ksp->vec_rhs);
     70:   return 0;
     71: }

     73: /*

     75:     KSPFGMRESCycle - Run fgmres, possibly with restart.  Return residual
     76:                   history if requested.

     78:     input parameters:
     79: .        fgmres  - structure containing parameters and work areas

     81:     output parameters:
     82: .        itcount - number of iterations used.  If null, ignored.
     83: .        converged - 0 if not converged

     85:     Notes:
     86:     On entry, the value in vector VEC_VV(0) should be
     87:     the initial residual.

     89:  */
     90: PetscErrorCode KSPFGMRESCycle(PetscInt *itcount,KSP ksp)
     91: {

     93:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)(ksp->data);
     94:   PetscReal      res_norm;
     95:   PetscReal      hapbnd,tt;
     96:   PetscBool      hapend = PETSC_FALSE;  /* indicates happy breakdown ending */
     97:   PetscInt       loc_it;                /* local count of # of dir. in Krylov space */
     98:   PetscInt       max_k = fgmres->max_k; /* max # of directions Krylov space */
     99:   Mat            Amat,Pmat;

    101:   /* Number of pseudo iterations since last restart is the number
    102:      of prestart directions */
    103:   loc_it = 0;

    105:   /* note: (fgmres->it) is always set one less than (loc_it) It is used in
    106:      KSPBUILDSolution_FGMRES, where it is passed to KSPFGMRESBuildSoln.
    107:      Note that when KSPFGMRESBuildSoln is called from this function,
    108:      (loc_it -1) is passed, so the two are equivalent */
    109:   fgmres->it = (loc_it - 1);

    111:   /* initial residual is in VEC_VV(0)  - compute its norm*/
    112:   VecNorm(VEC_VV(0),NORM_2,&res_norm);
    113:   KSPCheckNorm(ksp,res_norm);

    115:   /* first entry in right-hand-side of hessenberg system is just
    116:      the initial residual norm */
    117:   *RS(0) = res_norm;

    119:   ksp->rnorm = res_norm;
    120:   KSPLogResidualHistory(ksp,res_norm);
    121:   KSPMonitor(ksp,ksp->its,res_norm);

    123:   /* check for the convergence - maybe the current guess is good enough */
    124:   (*ksp->converged)(ksp,ksp->its,res_norm,&ksp->reason,ksp->cnvP);
    125:   if (ksp->reason) {
    126:     if (itcount) *itcount = 0;
    127:     return 0;
    128:   }

    130:   /* scale VEC_VV (the initial residual) */
    131:   VecScale(VEC_VV(0),1.0/res_norm);

    133:   /* MAIN ITERATION LOOP BEGINNING*/
    134:   /* keep iterating until we have converged OR generated the max number
    135:      of directions OR reached the max number of iterations for the method */
    136:   while (!ksp->reason && loc_it < max_k && ksp->its < ksp->max_it) {
    137:     if (loc_it) {
    138:       KSPLogResidualHistory(ksp,res_norm);
    139:       KSPMonitor(ksp,ksp->its,res_norm);
    140:     }
    141:     fgmres->it = (loc_it - 1);

    143:     /* see if more space is needed for work vectors */
    144:     if (fgmres->vv_allocated <= loc_it + VEC_OFFSET + 1) {
    145:       KSPFGMRESGetNewVectors(ksp,loc_it+1);
    146:       /* (loc_it+1) is passed in as number of the first vector that should
    147:          be allocated */
    148:     }

    150:     /* CHANGE THE PRECONDITIONER? */
    151:     /* ModifyPC is the callback function that can be used to
    152:        change the PC or its attributes before its applied */
    153:     (*fgmres->modifypc)(ksp,ksp->its,loc_it,res_norm,fgmres->modifyctx);

    155:     /* apply PRECONDITIONER to direction vector and store with
    156:        preconditioned vectors in prevec */
    157:     KSP_PCApply(ksp,VEC_VV(loc_it),PREVEC(loc_it));

    159:     PCGetOperators(ksp->pc,&Amat,&Pmat);
    160:     /* Multiply preconditioned vector by operator - put in VEC_VV(loc_it+1) */
    161:     KSP_MatMult(ksp,Amat,PREVEC(loc_it),VEC_VV(1+loc_it));

    163:     /* update hessenberg matrix and do Gram-Schmidt - new direction is in
    164:        VEC_VV(1+loc_it)*/
    165:     (*fgmres->orthog)(ksp,loc_it);

    167:     /* new entry in hessenburg is the 2-norm of our new direction */
    168:     VecNorm(VEC_VV(loc_it+1),NORM_2,&tt);
    169:     KSPCheckNorm(ksp,tt);

    171:     *HH(loc_it+1,loc_it)  = tt;
    172:     *HES(loc_it+1,loc_it) = tt;

    174:     /* Happy Breakdown Check */
    175:     hapbnd = PetscAbsScalar((tt) / *RS(loc_it));
    176:     /* RS(loc_it) contains the res_norm from the last iteration  */
    177:     hapbnd = PetscMin(fgmres->haptol,hapbnd);
    178:     if (tt > hapbnd) {
    179:       /* scale new direction by its norm */
    180:       VecScale(VEC_VV(loc_it+1),1.0/tt);
    181:     } else {
    182:       /* This happens when the solution is exactly reached. */
    183:       /* So there is no new direction... */
    184:       VecSet(VEC_TEMP,0.0);     /* set VEC_TEMP to 0 */
    185:       hapend = PETSC_TRUE;
    186:     }
    187:     /* note that for FGMRES we could get HES(loc_it+1, loc_it)  = 0 and the
    188:        current solution would not be exact if HES was singular.  Note that
    189:        HH non-singular implies that HES is no singular, and HES is guaranteed
    190:        to be nonsingular when PREVECS are linearly independent and A is
    191:        nonsingular (in GMRES, the nonsingularity of A implies the nonsingularity
    192:        of HES). So we should really add a check to verify that HES is nonsingular.*/

    194:     /* Now apply rotations to new col of hessenberg (and right side of system),
    195:        calculate new rotation, and get new residual norm at the same time*/
    196:     KSPFGMRESUpdateHessenberg(ksp,loc_it,hapend,&res_norm);
    197:     if (ksp->reason) break;

    199:     loc_it++;
    200:     fgmres->it = (loc_it-1);   /* Add this here in case it has converged */

    202:     PetscObjectSAWsTakeAccess((PetscObject)ksp);
    203:     ksp->its++;
    204:     ksp->rnorm = res_norm;
    205:     PetscObjectSAWsGrantAccess((PetscObject)ksp);

    207:     (*ksp->converged)(ksp,ksp->its,res_norm,&ksp->reason,ksp->cnvP);

    209:     /* Catch error in happy breakdown and signal convergence and break from loop */
    210:     if (hapend) {
    211:       if (!ksp->reason) {
    213:         else {
    214:           ksp->reason = KSP_DIVERGED_BREAKDOWN;
    215:           break;
    216:         }
    217:       }
    218:     }
    219:   }
    220:   /* END OF ITERATION LOOP */
    221:   KSPLogResidualHistory(ksp,res_norm);

    223:   /*
    224:      Monitor if we know that we will not return for a restart */
    225:   if (loc_it && (ksp->reason || ksp->its >= ksp->max_it)) {
    226:     KSPMonitor(ksp,ksp->its,res_norm);
    227:   }

    229:   if (itcount) *itcount = loc_it;

    231:   /*
    232:     Down here we have to solve for the "best" coefficients of the Krylov
    233:     columns, add the solution values together, and possibly unwind the
    234:     preconditioning from the solution
    235:    */

    237:   /* Form the solution (or the solution so far) */
    238:   /* Note: must pass in (loc_it-1) for iteration count so that KSPFGMRESBuildSoln
    239:      properly navigates */

    241:   KSPFGMRESBuildSoln(RS(0),ksp->vec_sol,ksp->vec_sol,ksp,loc_it-1);
    242:   return 0;
    243: }

    245: /*
    246:     KSPSolve_FGMRES - This routine applies the FGMRES method.

    248:    Input Parameter:
    249: .     ksp - the Krylov space object that was set to use fgmres

    251:    Output Parameter:
    252: .     outits - number of iterations used

    254: */

    256: PetscErrorCode KSPSolve_FGMRES(KSP ksp)
    257: {
    258:   PetscInt       cycle_its = 0; /* iterations done in a call to KSPFGMRESCycle */
    259:   KSP_FGMRES     *fgmres   = (KSP_FGMRES*)ksp->data;
    260:   PetscBool      diagonalscale;

    262:   PCGetDiagonalScale(ksp->pc,&diagonalscale);

    265:   PetscObjectSAWsTakeAccess((PetscObject)ksp);
    266:   ksp->its = 0;
    267:   PetscObjectSAWsGrantAccess((PetscObject)ksp);

    269:   /* Compute the initial (NOT preconditioned) residual */
    270:   if (!ksp->guess_zero) {
    271:     KSPFGMRESResidual(ksp);
    272:   } else { /* guess is 0 so residual is F (which is in ksp->vec_rhs) */
    273:     VecCopy(ksp->vec_rhs,VEC_VV(0));
    274:   }
    275:   /* This may be true only on a subset of MPI ranks; setting it here so it will be detected by the first norm computaion in the Krylov method */
    276:   if (ksp->reason == KSP_DIVERGED_PC_FAILED) {
    277:     VecSetInf(VEC_VV(0));
    278:   }

    280:   /* now the residual is in VEC_VV(0) - which is what
    281:      KSPFGMRESCycle expects... */

    283:   KSPFGMRESCycle(&cycle_its,ksp);
    284:   while (!ksp->reason) {
    285:     KSPFGMRESResidual(ksp);
    286:     if (ksp->its >= ksp->max_it) break;
    287:     KSPFGMRESCycle(&cycle_its,ksp);
    288:   }
    289:   /* mark lack of convergence */
    290:   if (ksp->its >= ksp->max_it && !ksp->reason) ksp->reason = KSP_DIVERGED_ITS;
    291:   return 0;
    292: }

    294: extern PetscErrorCode KSPReset_FGMRES(KSP);
    295: /*

    297:    KSPDestroy_FGMRES - Frees all memory space used by the Krylov method.

    299: */
    300: PetscErrorCode KSPDestroy_FGMRES(KSP ksp)
    301: {
    302:   KSPReset_FGMRES(ksp);
    303:   PetscObjectComposeFunction((PetscObject)ksp,"KSPFGMRESSetModifyPC_C",NULL);
    304:   KSPDestroy_GMRES(ksp);
    305:   return 0;
    306: }

    308: /*
    309:     KSPFGMRESBuildSoln - create the solution from the starting vector and the
    310:                       current iterates.

    312:     Input parameters:
    313:         nrs - work area of size it + 1.
    314:         vguess  - index of initial guess
    315:         vdest - index of result.  Note that vguess may == vdest (replace
    316:                 guess with the solution).
    317:         it - HH upper triangular part is a block of size (it+1) x (it+1)

    319:      This is an internal routine that knows about the FGMRES internals.
    320:  */
    321: static PetscErrorCode KSPFGMRESBuildSoln(PetscScalar *nrs,Vec vguess,Vec vdest,KSP ksp,PetscInt it)
    322: {
    323:   PetscScalar    tt;
    324:   PetscInt       ii,k,j;
    325:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)(ksp->data);

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

    329:   /* If it is < 0, no fgmres steps have been performed */
    330:   if (it < 0) {
    331:     VecCopy(vguess,vdest); /* VecCopy() is smart, exists immediately if vguess == vdest */
    332:     return 0;
    333:   }

    335:   /* so fgmres steps HAVE been performed */

    337:   /* solve the upper triangular system - RS is the right side and HH is
    338:      the upper triangular matrix  - put soln in nrs */
    339:   if (*HH(it,it) != 0.0) {
    340:     nrs[it] = *RS(it) / *HH(it,it);
    341:   } else {
    342:     nrs[it] = 0.0;
    343:   }
    344:   for (ii=1; ii<=it; ii++) {
    345:     k  = it - ii;
    346:     tt = *RS(k);
    347:     for (j=k+1; j<=it; j++) tt = tt - *HH(k,j) * nrs[j];
    348:     nrs[k] = tt / *HH(k,k);
    349:   }

    351:   /* Accumulate the correction to the soln of the preconditioned prob. in
    352:      VEC_TEMP - note that we use the preconditioned vectors  */
    353:   VecSet(VEC_TEMP,0.0); /* set VEC_TEMP components to 0 */
    354:   VecMAXPY(VEC_TEMP,it+1,nrs,&PREVEC(0));

    356:   /* put updated solution into vdest.*/
    357:   if (vdest != vguess) {
    358:     VecCopy(VEC_TEMP,vdest);
    359:     VecAXPY(vdest,1.0,vguess);
    360:   } else { /* replace guess with solution */
    361:     VecAXPY(vdest,1.0,VEC_TEMP);
    362:   }
    363:   return 0;
    364: }

    366: /*

    368:     KSPFGMRESUpdateHessenberg - Do the scalar work for the orthogonalization.
    369:                             Return new residual.

    371:     input parameters:

    373: .        ksp -    Krylov space object
    374: .        it  -    plane rotations are applied to the (it+1)th column of the
    375:                   modified hessenberg (i.e. HH(:,it))
    376: .        hapend - PETSC_FALSE not happy breakdown ending.

    378:     output parameters:
    379: .        res - the new residual

    381:  */
    382: static PetscErrorCode KSPFGMRESUpdateHessenberg(KSP ksp,PetscInt it,PetscBool hapend,PetscReal *res)
    383: {
    384:   PetscScalar *hh,*cc,*ss,tt;
    385:   PetscInt    j;
    386:   KSP_FGMRES  *fgmres = (KSP_FGMRES*)(ksp->data);

    388:   hh = HH(0,it);   /* pointer to beginning of column to update - so
    389:                       incrementing hh "steps down" the (it+1)th col of HH*/
    390:   cc = CC(0);      /* beginning of cosine rotations */
    391:   ss = SS(0);      /* beginning of sine rotations */

    393:   /* Apply all the previously computed plane rotations to the new column
    394:      of the Hessenberg matrix */
    395:   /* Note: this uses the rotation [conj(c)  s ; -s   c], c= cos(theta), s= sin(theta),
    396:      and some refs have [c   s ; -conj(s)  c] (don't be confused!) */

    398:   for (j=1; j<=it; j++) {
    399:     tt  = *hh;
    400:     *hh = PetscConj(*cc) * tt + *ss * *(hh+1);
    401:     hh++;
    402:     *hh = *cc++ * *hh - (*ss++ * tt);
    403:     /* hh, cc, and ss have all been incremented one by end of loop */
    404:   }

    406:   /*
    407:     compute the new plane rotation, and apply it to:
    408:      1) the right-hand-side of the Hessenberg system (RS)
    409:         note: it affects RS(it) and RS(it+1)
    410:      2) the new column of the Hessenberg matrix
    411:         note: it affects HH(it,it) which is currently pointed to
    412:         by hh and HH(it+1, it) (*(hh+1))
    413:     thus obtaining the updated value of the residual...
    414:   */

    416:   /* compute new plane rotation */

    418:   if (!hapend) {
    419:     tt = PetscSqrtScalar(PetscConj(*hh) * *hh + PetscConj(*(hh+1)) * *(hh+1));
    420:     if (tt == 0.0) {
    421:       ksp->reason = KSP_DIVERGED_NULL;
    422:       return 0;
    423:     }

    425:     *cc = *hh / tt;         /* new cosine value */
    426:     *ss = *(hh+1) / tt;        /* new sine value */

    428:     /* apply to 1) and 2) */
    429:     *RS(it+1) = -(*ss * *RS(it));
    430:     *RS(it)   = PetscConj(*cc) * *RS(it);
    431:     *hh       = PetscConj(*cc) * *hh + *ss * *(hh+1);

    433:     /* residual is the last element (it+1) of right-hand side! */
    434:     *res = PetscAbsScalar(*RS(it+1));

    436:   } else { /* happy breakdown: HH(it+1, it) = 0, therefore we don't need to apply
    437:             another rotation matrix (so RH doesn't change).  The new residual is
    438:             always the new sine term times the residual from last time (RS(it)),
    439:             but now the new sine rotation would be zero...so the residual should
    440:             be zero...so we will multiply "zero" by the last residual.  This might
    441:             not be exactly what we want to do here -could just return "zero". */

    443:     *res = 0.0;
    444:   }
    445:   return 0;
    446: }

    448: /*

    450:    KSPFGMRESGetNewVectors - This routine allocates more work vectors, starting from
    451:                          VEC_VV(it), and more preconditioned work vectors, starting
    452:                          from PREVEC(i).

    454: */
    455: static PetscErrorCode KSPFGMRESGetNewVectors(KSP ksp,PetscInt it)
    456: {
    457:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)ksp->data;
    458:   PetscInt       nwork   = fgmres->nwork_alloc; /* number of work vector chunks allocated */
    459:   PetscInt       nalloc;                      /* number to allocate */
    460:   PetscInt       k;

    462:   nalloc = fgmres->delta_allocate; /* number of vectors to allocate
    463:                                       in a single chunk */

    465:   /* Adjust the number to allocate to make sure that we don't exceed the
    466:      number of available slots (fgmres->vecs_allocated)*/
    467:   if (it + VEC_OFFSET + nalloc >= fgmres->vecs_allocated) {
    468:     nalloc = fgmres->vecs_allocated - it - VEC_OFFSET;
    469:   }
    470:   if (!nalloc) return 0;

    472:   fgmres->vv_allocated += nalloc; /* vv_allocated is the number of vectors allocated */

    474:   /* work vectors */
    475:   KSPCreateVecs(ksp,nalloc,&fgmres->user_work[nwork],0,NULL);
    476:   PetscLogObjectParents(ksp,nalloc,fgmres->user_work[nwork]);
    477:   for (k=0; k < nalloc; k++) {
    478:     fgmres->vecs[it+VEC_OFFSET+k] = fgmres->user_work[nwork][k];
    479:   }
    480:   /* specify size of chunk allocated */
    481:   fgmres->mwork_alloc[nwork] = nalloc;

    483:   /* preconditioned vectors */
    484:   KSPCreateVecs(ksp,nalloc,&fgmres->prevecs_user_work[nwork],0,NULL);
    485:   PetscLogObjectParents(ksp,nalloc,fgmres->prevecs_user_work[nwork]);
    486:   for (k=0; k < nalloc; k++) {
    487:     fgmres->prevecs[it+k] = fgmres->prevecs_user_work[nwork][k];
    488:   }

    490:   /* increment the number of work vector chunks */
    491:   fgmres->nwork_alloc++;
    492:   return 0;
    493: }

    495: /*

    497:    KSPBuildSolution_FGMRES

    499:      Input Parameter:
    500: .     ksp - the Krylov space object
    501: .     ptr-

    503:    Output Parameter:
    504: .     result - the solution

    506:    Note: this calls KSPFGMRESBuildSoln - the same function that KSPFGMRESCycle
    507:    calls directly.

    509: */
    510: PetscErrorCode KSPBuildSolution_FGMRES(KSP ksp,Vec ptr,Vec *result)
    511: {
    512:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)ksp->data;

    514:   if (!ptr) {
    515:     if (!fgmres->sol_temp) {
    516:       VecDuplicate(ksp->vec_sol,&fgmres->sol_temp);
    517:       PetscLogObjectParent((PetscObject)ksp,(PetscObject)fgmres->sol_temp);
    518:     }
    519:     ptr = fgmres->sol_temp;
    520:   }
    521:   if (!fgmres->nrs) {
    522:     /* allocate the work area */
    523:     PetscMalloc1(fgmres->max_k,&fgmres->nrs);
    524:     PetscLogObjectMemory((PetscObject)ksp,fgmres->max_k*sizeof(PetscScalar));
    525:   }

    527:   KSPFGMRESBuildSoln(fgmres->nrs,ksp->vec_sol,ptr,ksp,fgmres->it);
    528:   if (result) *result = ptr;
    529:   return 0;
    530: }

    532: PetscErrorCode KSPSetFromOptions_FGMRES(PetscOptionItems *PetscOptionsObject,KSP ksp)
    533: {
    534:   PetscBool      flg;

    536:   KSPSetFromOptions_GMRES(PetscOptionsObject,ksp);
    537:   PetscOptionsHead(PetscOptionsObject,"KSP flexible GMRES Options");
    538:   PetscOptionsBoolGroupBegin("-ksp_fgmres_modifypcnochange","do not vary the preconditioner","KSPFGMRESSetModifyPC",&flg);
    539:   if (flg) KSPFGMRESSetModifyPC(ksp,KSPFGMRESModifyPCNoChange,NULL,NULL);
    540:   PetscOptionsBoolGroupEnd("-ksp_fgmres_modifypcksp","vary the KSP based preconditioner","KSPFGMRESSetModifyPC",&flg);
    541:   if (flg) KSPFGMRESSetModifyPC(ksp,KSPFGMRESModifyPCKSP,NULL,NULL);
    542:   PetscOptionsTail();
    543:   return 0;
    544: }

    546: typedef PetscErrorCode (*FCN1)(KSP,PetscInt,PetscInt,PetscReal,void*); /* force argument to next function to not be extern C*/
    547: typedef PetscErrorCode (*FCN2)(void*);

    549: static PetscErrorCode  KSPFGMRESSetModifyPC_FGMRES(KSP ksp,FCN1 fcn,void *ctx,FCN2 d)
    550: {
    552:   ((KSP_FGMRES*)ksp->data)->modifypc      = fcn;
    553:   ((KSP_FGMRES*)ksp->data)->modifydestroy = d;
    554:   ((KSP_FGMRES*)ksp->data)->modifyctx     = ctx;
    555:   return 0;
    556: }

    558: PetscErrorCode KSPReset_FGMRES(KSP ksp)
    559: {
    560:   KSP_FGMRES     *fgmres = (KSP_FGMRES*)ksp->data;
    561:   PetscInt       i;

    563:   PetscFree (fgmres->prevecs);
    564:   if (fgmres->nwork_alloc>0) {
    565:     i=0;
    566:     /* In the first allocation we allocated VEC_OFFSET fewer vectors in prevecs */
    567:     VecDestroyVecs(fgmres->mwork_alloc[i]-VEC_OFFSET,&fgmres->prevecs_user_work[i]);
    568:     for (i=1; i<fgmres->nwork_alloc; i++) {
    569:       VecDestroyVecs(fgmres->mwork_alloc[i],&fgmres->prevecs_user_work[i]);
    570:     }
    571:   }
    572:   PetscFree(fgmres->prevecs_user_work);
    573:   if (fgmres->modifydestroy) {
    574:     (*fgmres->modifydestroy)(fgmres->modifyctx);
    575:   }
    576:   KSPReset_GMRES(ksp);
    577:   return 0;
    578: }

    580: PetscErrorCode  KSPGMRESSetRestart_FGMRES(KSP ksp,PetscInt max_k)
    581: {
    582:   KSP_FGMRES     *gmres = (KSP_FGMRES*)ksp->data;

    585:   if (!ksp->setupstage) {
    586:     gmres->max_k = max_k;
    587:   } else if (gmres->max_k != max_k) {
    588:     gmres->max_k    = max_k;
    589:     ksp->setupstage = KSP_SETUP_NEW;
    590:     /* free the data structures, then create them again */
    591:     KSPReset_FGMRES(ksp);
    592:   }
    593:   return 0;
    594: }

    596: PetscErrorCode  KSPGMRESGetRestart_FGMRES(KSP ksp,PetscInt *max_k)
    597: {
    598:   KSP_FGMRES *gmres = (KSP_FGMRES*)ksp->data;

    600:   *max_k = gmres->max_k;
    601:   return 0;
    602: }

    604: /*MC
    605:      KSPFGMRES - Implements the Flexible Generalized Minimal Residual method.
    606:                 developed by Saad with restart

    608:    Options Database Keys:
    609: +   -ksp_gmres_restart <restart> - the number of Krylov directions to orthogonalize against
    610: .   -ksp_gmres_haptol <tol> - sets the tolerance for "happy ending" (exact convergence)
    611: .   -ksp_gmres_preallocate - preallocate all the Krylov search directions initially (otherwise groups of
    612:                              vectors are allocated as needed)
    613: .   -ksp_gmres_classicalgramschmidt - use classical (unmodified) Gram-Schmidt to orthogonalize against the Krylov space (fast) (the default)
    614: .   -ksp_gmres_modifiedgramschmidt - use modified Gram-Schmidt in the orthogonalization (more stable, but slower)
    615: .   -ksp_gmres_cgs_refinement_type <refine_never,refine_ifneeded,refine_always> - determine if iterative refinement is used to increase the
    616:                                    stability of the classical Gram-Schmidt  orthogonalization.
    617: .   -ksp_gmres_krylov_monitor - plot the Krylov space generated
    618: .   -ksp_fgmres_modifypcnochange - do not change the preconditioner between iterations
    619: -   -ksp_fgmres_modifypcksp - modify the preconditioner using KSPFGMRESModifyPCKSP()

    621:    Level: beginner

    623:     Notes:
    624:     See KSPFGMRESSetModifyPC() for how to vary the preconditioner between iterations
    625:            Only right preconditioning is supported.

    627:     Notes:
    628:     The following options -ksp_type fgmres -pc_type ksp -ksp_ksp_type bcgs -ksp_view -ksp_pc_type jacobi make the preconditioner (or inner solver)
    629:            be bi-CG-stab with a preconditioner of Jacobi.

    631:     Developer Notes:
    632:     This object is subclassed off of KSPGMRES

    634: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPGMRES, KSPLGMRES,
    635:            KSPGMRESSetRestart(), KSPGMRESSetHapTol(), KSPGMRESSetPreAllocateVectors(), KSPGMRESSetOrthogonalization(), KSPGMRESGetOrthogonalization(),
    636:            KSPGMRESClassicalGramSchmidtOrthogonalization(), KSPGMRESModifiedGramSchmidtOrthogonalization(),
    637:            KSPGMRESCGSRefinementType, KSPGMRESSetCGSRefinementType(),  KSPGMRESGetCGSRefinementType(), KSPGMRESMonitorKrylov(), KSPFGMRESSetModifyPC(),
    638:            KSPFGMRESModifyPCKSP()

    640: M*/

    642: PETSC_EXTERN PetscErrorCode KSPCreate_FGMRES(KSP ksp)
    643: {
    644:   KSP_FGMRES     *fgmres;

    646:   PetscNewLog(ksp,&fgmres);

    648:   ksp->data                              = (void*)fgmres;
    649:   ksp->ops->buildsolution                = KSPBuildSolution_FGMRES;
    650:   ksp->ops->setup                        = KSPSetUp_FGMRES;
    651:   ksp->ops->solve                        = KSPSolve_FGMRES;
    652:   ksp->ops->reset                        = KSPReset_FGMRES;
    653:   ksp->ops->destroy                      = KSPDestroy_FGMRES;
    654:   ksp->ops->view                         = KSPView_GMRES;
    655:   ksp->ops->setfromoptions               = KSPSetFromOptions_FGMRES;
    656:   ksp->ops->computeextremesingularvalues = KSPComputeExtremeSingularValues_GMRES;
    657:   ksp->ops->computeeigenvalues           = KSPComputeEigenvalues_GMRES;

    659:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,3);
    660:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_RIGHT,1);

    662:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetPreAllocateVectors_C",KSPGMRESSetPreAllocateVectors_GMRES);
    663:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetOrthogonalization_C",KSPGMRESSetOrthogonalization_GMRES);
    664:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetOrthogonalization_C",KSPGMRESGetOrthogonalization_GMRES);
    665:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetRestart_C",KSPGMRESSetRestart_FGMRES);
    666:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetRestart_C",KSPGMRESGetRestart_FGMRES);
    667:   PetscObjectComposeFunction((PetscObject)ksp,"KSPFGMRESSetModifyPC_C",KSPFGMRESSetModifyPC_FGMRES);
    668:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESSetCGSRefinementType_C",KSPGMRESSetCGSRefinementType_GMRES);
    669:   PetscObjectComposeFunction((PetscObject)ksp,"KSPGMRESGetCGSRefinementType_C",KSPGMRESGetCGSRefinementType_GMRES);

    671:   fgmres->haptol         = 1.0e-30;
    672:   fgmres->q_preallocate  = 0;
    673:   fgmres->delta_allocate = FGMRES_DELTA_DIRECTIONS;
    674:   fgmres->orthog         = KSPGMRESClassicalGramSchmidtOrthogonalization;
    675:   fgmres->nrs            = NULL;
    676:   fgmres->sol_temp       = NULL;
    677:   fgmres->max_k          = FGMRES_DEFAULT_MAXK;
    678:   fgmres->Rsvd           = NULL;
    679:   fgmres->orthogwork     = NULL;
    680:   fgmres->modifypc       = KSPFGMRESModifyPCNoChange;
    681:   fgmres->modifyctx      = NULL;
    682:   fgmres->modifydestroy  = NULL;
    683:   fgmres->cgstype        = KSP_GMRES_CGS_REFINE_NEVER;
    684:   return 0;
    685: }