Date: 2026-03-01T05:24:48+00:00

Actual source code: pgmres.c

      1: /*
      2:     This file implements PGMRES (a Pipelined Generalized Minimal Residual method)
      3: */

      5: #include <../src/ksp/ksp/impls/gmres/pgmres/pgmresimpl.h>

      7: static PetscErrorCode KSPPGMRESUpdateHessenberg(KSP, PetscInt, PetscBool *, PetscReal *);
      8: static PetscErrorCode KSPPGMRESBuildSoln(PetscScalar *, Vec, Vec, KSP, PetscInt);

     10: static PetscErrorCode KSPSetUp_PGMRES(KSP ksp)
     11: {
     12:   PetscFunctionBegin;
     13:   PetscCall(KSPSetUp_GMRES(ksp));
     14:   PetscFunctionReturn(PETSC_SUCCESS);
     15: }

     17: static PetscErrorCode KSPPGMRESCycle(PetscInt *itcount, KSP ksp)
     18: {
     19:   KSP_PGMRES *pgmres = (KSP_PGMRES *)ksp->data;
     20:   PetscReal   res_norm, res, newnorm;
     21:   PetscInt    it     = 0, j, k;
     22:   PetscBool   hapend = PETSC_FALSE;

     24:   PetscFunctionBegin;
     25:   if (itcount) *itcount = 0;
     26:   PetscCall(VecNormalize(VEC_VV(0), &res_norm));
     27:   KSPCheckNorm(ksp, res_norm);
     28:   res    = res_norm;
     29:   *RS(0) = res_norm;

     31:   /* check for the convergence */
     32:   PetscCall(PetscObjectSAWsTakeAccess((PetscObject)ksp));
     33:   if (ksp->normtype != KSP_NORM_NONE) ksp->rnorm = res;
     34:   else ksp->rnorm = 0;
     35:   PetscCall(PetscObjectSAWsGrantAccess((PetscObject)ksp));
     36:   pgmres->it = it - 2;
     37:   PetscCall(KSPLogResidualHistory(ksp, ksp->rnorm));
     38:   PetscCall(KSPMonitor(ksp, ksp->its, ksp->rnorm));
     39:   if (!res) {
     40:     ksp->reason = KSP_CONVERGED_ATOL;
     41:     PetscCall(PetscInfo(ksp, "Converged due to zero residual norm on entry\n"));
     42:     PetscFunctionReturn(PETSC_SUCCESS);
     43:   }

     45:   PetscCall((*ksp->converged)(ksp, ksp->its, ksp->rnorm, &ksp->reason, ksp->cnvP));
     46:   for (; !ksp->reason; it++) {
     47:     Vec Zcur, Znext;
     48:     if (pgmres->vv_allocated <= it + VEC_OFFSET + 1) PetscCall(KSPGMRESGetNewVectors(ksp, it + 1));
     49:     /* VEC_VV(it-1) is orthogonal, it will be normalized once the VecNorm arrives. */
     50:     Zcur  = VEC_VV(it);     /* Zcur is not yet orthogonal, but the VecMDot to orthogonalize it has been started. */
     51:     Znext = VEC_VV(it + 1); /* This iteration will compute Znext, update with a deferred correction once we know how
     52:                                Zcur relates to the previous vectors, and start the reduction to orthogonalize it. */

     54:     if (it < pgmres->max_k + 1 && ksp->its + 1 < PetscMax(2, ksp->max_it)) { /* We don't know whether what we have computed is enough, so apply the matrix. */
     55:       PetscCall(KSP_PCApplyBAorAB(ksp, Zcur, Znext, VEC_TEMP_MATOP));
     56:     }

     58:     if (it > 1) { /* Complete the pending reduction */
     59:       PetscCall(VecNormEnd(VEC_VV(it - 1), NORM_2, &newnorm));
     60:       *HH(it - 1, it - 2) = newnorm;
     61:     }
     62:     if (it > 0) { /* Finish the reduction computing the latest column of H */
     63:       PetscCall(VecMDotEnd(Zcur, it, &(VEC_VV(0)), HH(0, it - 1)));
     64:     }

     66:     if (it > 1) {
     67:       /* normalize the base vector from two iterations ago, basis is complete up to here */
     68:       PetscCall(VecScale(VEC_VV(it - 1), 1. / *HH(it - 1, it - 2)));

     70:       PetscCall(KSPPGMRESUpdateHessenberg(ksp, it - 2, &hapend, &res));
     71:       pgmres->it = it - 2;
     72:       ksp->its++;
     73:       if (ksp->normtype != KSP_NORM_NONE) ksp->rnorm = res;
     74:       else ksp->rnorm = 0;

     76:       PetscCall((*ksp->converged)(ksp, ksp->its, ksp->rnorm, &ksp->reason, ksp->cnvP));
     77:       if (ksp->reason) break;
     78:       if (it < pgmres->max_k + 1) { /* Monitor if we are not done or still iterating, but not before a restart. */
     79:         PetscCall(KSPLogResidualHistory(ksp, ksp->rnorm));
     80:         PetscCall(KSPMonitor(ksp, ksp->its, ksp->rnorm));
     81:       }
     82:       /* Catch error in happy breakdown and signal convergence and break from loop */
     83:       if (hapend) {
     84:         PetscCheck(!ksp->errorifnotconverged, PetscObjectComm((PetscObject)ksp), PETSC_ERR_NOT_CONVERGED, "Reached happy break down, but convergence was not indicated. Residual norm = %g", (double)res);
     85:         ksp->reason = KSP_DIVERGED_BREAKDOWN;
     86:         break;
     87:       }

     89:       if (!(it < pgmres->max_k + 1 && ksp->its < ksp->max_it)) break;

     91:       /* The it-2 column of H was not scaled when we computed Zcur, apply correction */
     92:       PetscCall(VecScale(Zcur, 1. / *HH(it - 1, it - 2)));
     93:       /* And Znext computed in this iteration was computed using the under-scaled Zcur */
     94:       PetscCall(VecScale(Znext, 1. / *HH(it - 1, it - 2)));

     96:       /* In the previous iteration, we projected an unnormalized Zcur against the Krylov basis, so we need to fix the column of H resulting from that projection. */
     97:       for (k = 0; k < it; k++) *HH(k, it - 1) /= *HH(it - 1, it - 2);
     98:       /* When Zcur was projected against the Krylov basis, VV(it-1) was still not normalized, so fix that too. This
     99:        * column is complete except for HH(it,it-1) which we won't know until the next iteration. */
    100:       *HH(it - 1, it - 1) /= *HH(it - 1, it - 2);
    101:     }

    103:     if (it > 0) {
    104:       PetscScalar *work;
    105:       if (!pgmres->orthogwork) PetscCall(PetscMalloc1(pgmres->max_k + 2, &pgmres->orthogwork));
    106:       work = pgmres->orthogwork;
    107:       /* Apply correction computed by the VecMDot in the last iteration to Znext. The original form is
    108:        *
    109:        *   Znext -= sum_{j=0}^{i-1} Z[j+1] * H[j,i-1]
    110:        *
    111:        * where
    112:        *
    113:        *   Z[j] = sum_{k=0}^j V[k] * H[k,j-1]
    114:        *
    115:        * substituting
    116:        *
    117:        *   Znext -= sum_{j=0}^{i-1} sum_{k=0}^{j+1} V[k] * H[k,j] * H[j,i-1]
    118:        *
    119:        * rearranging the iteration space from row-column to column-row
    120:        *
    121:        *   Znext -= sum_{k=0}^i sum_{j=k-1}^{i-1} V[k] * H[k,j] * H[j,i-1]
    122:        *
    123:        * Note that column it-1 of HH is correct. For all previous columns, we must look at HES because HH has already
    124:        * been transformed to upper triangular form.
    125:        */
    126:       for (k = 0; k < it + 1; k++) {
    127:         work[k] = 0;
    128:         for (j = PetscMax(0, k - 1); j < it - 1; j++) work[k] -= *HES(k, j) * *HH(j, it - 1);
    129:       }
    130:       PetscCall(VecMAXPY(Znext, it + 1, work, &VEC_VV(0)));
    131:       PetscCall(VecAXPY(Znext, -*HH(it - 1, it - 1), Zcur));

    133:       /* Orthogonalize Zcur against existing basis vectors. */
    134:       for (k = 0; k < it; k++) work[k] = -*HH(k, it - 1);
    135:       PetscCall(VecMAXPY(Zcur, it, work, &VEC_VV(0)));
    136:       /* Zcur is now orthogonal, and will be referred to as VEC_VV(it) again, though it is still not normalized. */
    137:       /* Begin computing the norm of the new vector, will be normalized after the MatMult in the next iteration. */
    138:       PetscCall(VecNormBegin(VEC_VV(it), NORM_2, &newnorm));
    139:     }

    141:     /* Compute column of H (to the diagonal, but not the subdiagonal) to be able to orthogonalize the newest vector. */
    142:     PetscCall(VecMDotBegin(Znext, it + 1, &VEC_VV(0), HH(0, it)));

    144:     /* Start an asynchronous split-mode reduction, the result of the MDot and Norm will be collected on the next iteration. */
    145:     PetscCall(PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)Znext)));
    146:   }
    147:   if (itcount) *itcount = it - 1; /* Number of iterations actually completed. */

    149:   /*
    150:     Solve for the "best" coefficients of the Krylov
    151:     columns, add the solution values together, and possibly unwind the preconditioning from the solution
    152:    */
    153:   /* Form the solution (or the solution so far) */
    154:   PetscCall(KSPPGMRESBuildSoln(RS(0), ksp->vec_sol, ksp->vec_sol, ksp, it - 2));

    156:   if (ksp->reason == KSP_CONVERGED_ITERATING && ksp->its == ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
    157:   if (ksp->reason) {
    158:     PetscCall(KSPLogResidualHistory(ksp, ksp->rnorm));
    159:     PetscCall(KSPMonitor(ksp, ksp->its, ksp->rnorm));
    160:   }
    161:   PetscFunctionReturn(PETSC_SUCCESS);
    162: }

    164: static PetscErrorCode KSPSolve_PGMRES(KSP ksp)
    165: {
    166:   PetscInt    its, itcount;
    167:   KSP_PGMRES *pgmres     = (KSP_PGMRES *)ksp->data;
    168:   PetscBool   guess_zero = ksp->guess_zero;

    170:   PetscFunctionBegin;
    171:   PetscCheck(!ksp->calc_sings || pgmres->Rsvd, PetscObjectComm((PetscObject)ksp), PETSC_ERR_ORDER, "Must call KSPSetComputeSingularValues() before KSPSetUp() is called");
    172:   PetscCall(PetscObjectSAWsTakeAccess((PetscObject)ksp));
    173:   ksp->its = 0;
    174:   PetscCall(PetscObjectSAWsGrantAccess((PetscObject)ksp));

    176:   itcount     = 0;
    177:   ksp->reason = KSP_CONVERGED_ITERATING;
    178:   while (!ksp->reason) {
    179:     PetscCall(KSPInitialResidual(ksp, ksp->vec_sol, VEC_TEMP, VEC_TEMP_MATOP, VEC_VV(0), ksp->vec_rhs));
    180:     PetscCall(KSPPGMRESCycle(&its, ksp));
    181:     itcount += its;
    182:     if (itcount >= ksp->max_it) {
    183:       if (!ksp->reason) ksp->reason = KSP_DIVERGED_ITS;
    184:       break;
    185:     }
    186:     ksp->guess_zero = PETSC_FALSE; /* every future call to KSPInitialResidual() will have nonzero guess */
    187:   }
    188:   ksp->guess_zero = guess_zero; /* restore if user provided nonzero initial guess */
    189:   PetscFunctionReturn(PETSC_SUCCESS);
    190: }

    192: static PetscErrorCode KSPDestroy_PGMRES(KSP ksp)
    193: {
    194:   PetscFunctionBegin;
    195:   PetscCall(KSPDestroy_GMRES(ksp));
    196:   PetscFunctionReturn(PETSC_SUCCESS);
    197: }

    199: static PetscErrorCode KSPPGMRESBuildSoln(PetscScalar *nrs, Vec vguess, Vec vdest, KSP ksp, PetscInt it)
    200: {
    201:   PetscScalar tt;
    202:   PetscInt    k, j;
    203:   KSP_PGMRES *pgmres = (KSP_PGMRES *)ksp->data;

    205:   PetscFunctionBegin;
    206:   /* Solve for solution vector that minimizes the residual */

    208:   if (it < 0) {                        /* no pgmres steps have been performed */
    209:     PetscCall(VecCopy(vguess, vdest)); /* VecCopy() is smart, exits immediately if vguess == vdest */
    210:     PetscFunctionReturn(PETSC_SUCCESS);
    211:   }

    213:   /* solve the upper triangular system - RS is the right side and HH is
    214:      the upper triangular matrix  - put soln in nrs */
    215:   if (*HH(it, it) != 0.0) nrs[it] = *RS(it) / *HH(it, it);
    216:   else nrs[it] = 0.0;

    218:   for (k = it - 1; k >= 0; k--) {
    219:     tt = *RS(k);
    220:     for (j = k + 1; j <= it; j++) tt -= *HH(k, j) * nrs[j];
    221:     nrs[k] = tt / *HH(k, k);
    222:   }

    224:   /* Accumulate the correction to the solution of the preconditioned problem in TEMP */
    225:   PetscCall(VecMAXPBY(VEC_TEMP, it + 1, nrs, 0, &VEC_VV(0)));
    226:   PetscCall(KSPUnwindPreconditioner(ksp, VEC_TEMP, VEC_TEMP_MATOP));
    227:   /* add solution to previous solution */
    228:   if (vdest == vguess) {
    229:     PetscCall(VecAXPY(vdest, 1.0, VEC_TEMP));
    230:   } else {
    231:     PetscCall(VecWAXPY(vdest, 1.0, VEC_TEMP, vguess));
    232:   }
    233:   PetscFunctionReturn(PETSC_SUCCESS);
    234: }

    236: static PetscErrorCode KSPPGMRESUpdateHessenberg(KSP ksp, PetscInt it, PetscBool *hapend, PetscReal *res)
    237: {
    238:   PetscScalar *hh, *cc, *ss, *rs;
    239:   PetscInt     j;
    240:   PetscReal    hapbnd;
    241:   KSP_PGMRES  *pgmres = (KSP_PGMRES *)ksp->data;

    243:   PetscFunctionBegin;
    244:   hh = HH(0, it); /* pointer to beginning of column to update */
    245:   cc = CC(0);     /* beginning of cosine rotations */
    246:   ss = SS(0);     /* beginning of sine rotations */
    247:   rs = RS(0);     /* right-hand side of least squares system */

    249:   /* The Hessenberg matrix is now correct through column it, save that form for possible spectral analysis */
    250:   for (j = 0; j <= it + 1; j++) *HES(j, it) = hh[j];

    252:   /* check for the happy breakdown */
    253:   hapbnd = PetscMin(PetscAbsScalar(hh[it + 1] / rs[it]), pgmres->haptol);
    254:   if (PetscAbsScalar(hh[it + 1]) < hapbnd) {
    255:     PetscCall(PetscInfo(ksp, "Detected happy breakdown, current hapbnd = %14.12e H(%" PetscInt_FMT ",%" PetscInt_FMT ") = %14.12e\n", (double)hapbnd, it + 1, it, (double)PetscAbsScalar(*HH(it + 1, it))));
    256:     *hapend = PETSC_TRUE;
    257:   }

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

    263:   for (j = 0; j < it; j++) {
    264:     PetscScalar hhj = hh[j];
    265:     hh[j]           = PetscConj(cc[j]) * hhj + ss[j] * hh[j + 1];
    266:     hh[j + 1]       = -ss[j] * hhj + cc[j] * hh[j + 1];
    267:   }

    269:   /*
    270:     compute the new plane rotation, and apply it to:
    271:      1) the right-hand side of the Hessenberg system (RS)
    272:         note: it affects RS(it) and RS(it+1)
    273:      2) the new column of the Hessenberg matrix
    274:         note: it affects HH(it,it) which is currently pointed to
    275:         by hh and HH(it+1, it) (*(hh+1))
    276:     thus obtaining the updated value of the residual...
    277:   */

    279:   /* compute new plane rotation */

    281:   if (!*hapend) {
    282:     PetscReal delta = PetscSqrtReal(PetscSqr(PetscAbsScalar(hh[it])) + PetscSqr(PetscAbsScalar(hh[it + 1])));
    283:     if (delta == 0.0) {
    284:       ksp->reason = KSP_DIVERGED_NULL;
    285:       PetscFunctionReturn(PETSC_SUCCESS);
    286:     }

    288:     cc[it] = hh[it] / delta;     /* new cosine value */
    289:     ss[it] = hh[it + 1] / delta; /* new sine value */

    291:     hh[it]     = PetscConj(cc[it]) * hh[it] + ss[it] * hh[it + 1];
    292:     rs[it + 1] = -ss[it] * rs[it];
    293:     rs[it]     = PetscConj(cc[it]) * rs[it];
    294:     *res       = PetscAbsScalar(rs[it + 1]);
    295:   } else { /* happy breakdown: HH(it+1, it) = 0, therefore we don't need to apply
    296:             another rotation matrix (so RH doesn't change).  The new residual is
    297:             always the new sine term times the residual from last time (RS(it)),
    298:             but now the new sine rotation would be zero...so the residual should
    299:             be zero...so we will multiply "zero" by the last residual.  This might
    300:             not be exactly what we want to do here -could just return "zero". */
    301:     *res = 0.0;
    302:   }
    303:   PetscFunctionReturn(PETSC_SUCCESS);
    304: }

    306: static PetscErrorCode KSPBuildSolution_PGMRES(KSP ksp, Vec ptr, Vec *result)
    307: {
    308:   KSP_PGMRES *pgmres = (KSP_PGMRES *)ksp->data;

    310:   PetscFunctionBegin;
    311:   if (!ptr) {
    312:     if (!pgmres->sol_temp) PetscCall(VecDuplicate(ksp->vec_sol, &pgmres->sol_temp));
    313:     ptr = pgmres->sol_temp;
    314:   }
    315:   if (!pgmres->nrs) {
    316:     /* allocate the work area */
    317:     PetscCall(PetscMalloc1(pgmres->max_k, &pgmres->nrs));
    318:   }

    320:   PetscCall(KSPPGMRESBuildSoln(pgmres->nrs, ksp->vec_sol, ptr, ksp, pgmres->it));
    321:   if (result) *result = ptr;
    322:   PetscFunctionReturn(PETSC_SUCCESS);
    323: }

    325: static PetscErrorCode KSPSetFromOptions_PGMRES(KSP ksp, PetscOptionItems PetscOptionsObject)
    326: {
    327:   PetscFunctionBegin;
    328:   PetscCall(KSPSetFromOptions_GMRES(ksp, PetscOptionsObject));
    329:   PetscOptionsHeadBegin(PetscOptionsObject, "KSP pipelined GMRES Options");
    330:   PetscOptionsHeadEnd();
    331:   PetscFunctionReturn(PETSC_SUCCESS);
    332: }

    334: static PetscErrorCode KSPReset_PGMRES(KSP ksp)
    335: {
    336:   PetscFunctionBegin;
    337:   PetscCall(KSPReset_GMRES(ksp));
    338:   PetscFunctionReturn(PETSC_SUCCESS);
    339: }

    341: /*MC
    342:    KSPPGMRES - Implements the Pipelined Generalized Minimal Residual method {cite}`ghyselsashbymeerbergenvanroose2013`. [](sec_pipelineksp)

    344:    Options Database Keys:
    345: +   -ksp_gmres_restart <restart>                                                - the number of Krylov directions to orthogonalize against
    346: .   -ksp_gmres_haptol <tol>                                                     - sets the tolerance for "happy ending" (exact convergence)
    347: .   -ksp_gmres_preallocate                                                      - preallocate all the Krylov search directions initially
    348:                                                                                 (otherwise groups of vectors are allocated as needed)
    349: .   -ksp_gmres_classicalgramschmidt                                             - use classical (unmodified) Gram-Schmidt to orthogonalize
    350:                                                                                 against the Krylov space (fast) (the default)
    351: .   -ksp_gmres_modifiedgramschmidt                                              - use modified Gram-Schmidt in the orthogonalization (more stable, but slower)
    352: .   -ksp_gmres_cgs_refinement_type <refine_never,refine_ifneeded,refine_always> - determine if iterative refinement is used to increase the
    353:                                                                                 stability of the classical Gram-Schmidt  orthogonalization.
    354: -   -ksp_gmres_krylov_monitor                                                   - plot the Krylov space generated

    356:    Level: beginner

    358:    Note:
    359:    MPI configuration may be necessary for reductions to make asynchronous progress, which is important for performance of pipelined methods.
    360:    See [](doc_faq_pipelined)

    362:    Developer Note:
    363:    This object is subclassed off of `KSPGMRES`, see the source code in src/ksp/ksp/impls/gmres for comments on the structure of the code

    365: .seealso: [](ch_ksp), [](sec_pipelineksp), [](doc_faq_pipelined), `KSPCreate()`, `KSPSetType()`, `KSPType`, `KSP`, `KSPGMRES`, `KSPLGMRES`, `KSPPIPECG`, `KSPPIPECR`,
    366:           `KSPGMRESSetRestart()`, `KSPGMRESSetHapTol()`, `KSPGMRESSetPreAllocateVectors()`, `KSPGMRESSetOrthogonalization()`, `KSPGMRESGetOrthogonalization()`,
    367:           `KSPGMRESClassicalGramSchmidtOrthogonalization()`, `KSPGMRESModifiedGramSchmidtOrthogonalization()`,
    368:           `KSPGMRESCGSRefinementType`, `KSPGMRESSetCGSRefinementType()`, `KSPGMRESGetCGSRefinementType()`, `KSPGMRESMonitorKrylov()`
    369: M*/

    371: PETSC_EXTERN PetscErrorCode KSPCreate_PGMRES(KSP ksp)
    372: {
    373:   KSP_PGMRES *pgmres;

    375:   PetscFunctionBegin;
    376:   PetscCall(PetscNew(&pgmres));

    378:   ksp->data                              = (void *)pgmres;
    379:   ksp->ops->buildsolution                = KSPBuildSolution_PGMRES;
    380:   ksp->ops->setup                        = KSPSetUp_PGMRES;
    381:   ksp->ops->solve                        = KSPSolve_PGMRES;
    382:   ksp->ops->reset                        = KSPReset_PGMRES;
    383:   ksp->ops->destroy                      = KSPDestroy_PGMRES;
    384:   ksp->ops->view                         = KSPView_GMRES;
    385:   ksp->ops->setfromoptions               = KSPSetFromOptions_PGMRES;
    386:   ksp->ops->computeextremesingularvalues = KSPComputeExtremeSingularValues_GMRES;
    387:   ksp->ops->computeeigenvalues           = KSPComputeEigenvalues_GMRES;

    389:   PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_PRECONDITIONED, PC_LEFT, 3));
    390:   PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_UNPRECONDITIONED, PC_RIGHT, 2));
    391:   PetscCall(KSPSetSupportedNorm(ksp, KSP_NORM_NONE, PC_RIGHT, 1));

    393:   PetscCall(PetscObjectComposeFunction((PetscObject)ksp, "KSPGMRESSetPreAllocateVectors_C", KSPGMRESSetPreAllocateVectors_GMRES));
    394:   PetscCall(PetscObjectComposeFunction((PetscObject)ksp, "KSPGMRESSetOrthogonalization_C", KSPGMRESSetOrthogonalization_GMRES));
    395:   PetscCall(PetscObjectComposeFunction((PetscObject)ksp, "KSPGMRESGetOrthogonalization_C", KSPGMRESGetOrthogonalization_GMRES));
    396:   PetscCall(PetscObjectComposeFunction((PetscObject)ksp, "KSPGMRESSetRestart_C", KSPGMRESSetRestart_GMRES));
    397:   PetscCall(PetscObjectComposeFunction((PetscObject)ksp, "KSPGMRESGetRestart_C", KSPGMRESGetRestart_GMRES));
    398:   PetscCall(PetscObjectComposeFunction((PetscObject)ksp, "KSPGMRESSetCGSRefinementType_C", KSPGMRESSetCGSRefinementType_GMRES));
    399:   PetscCall(PetscObjectComposeFunction((PetscObject)ksp, "KSPGMRESGetCGSRefinementType_C", KSPGMRESGetCGSRefinementType_GMRES));

    401:   pgmres->nextra_vecs    = 1;
    402:   pgmres->haptol         = 1.0e-30;
    403:   pgmres->q_preallocate  = 0;
    404:   pgmres->delta_allocate = PGMRES_DELTA_DIRECTIONS;
    405:   pgmres->orthog         = KSPGMRESClassicalGramSchmidtOrthogonalization;
    406:   pgmres->nrs            = NULL;
    407:   pgmres->sol_temp       = NULL;
    408:   pgmres->max_k          = PGMRES_DEFAULT_MAXK;
    409:   pgmres->Rsvd           = NULL;
    410:   pgmres->orthogwork     = NULL;
    411:   pgmres->cgstype        = KSP_GMRES_CGS_REFINE_NEVER;
    412:   PetscFunctionReturn(PETSC_SUCCESS);
    413: }