Actual source code: snesngmres.c

petsc-3.6.1 2015-07-22
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  1: #include <../src/snes/impls/ngmres/snesngmres.h> /*I "petscsnes.h" I*/
  2: #include <petscblaslapack.h>
  3: #include <petscdm.h>

  5: const char *const SNESNGMRESRestartTypes[] = {"NONE","PERIODIC","DIFFERENCE","SNESNGMRESRestartType","SNES_NGMRES_RESTART_",0};
  6: const char *const SNESNGMRESSelectTypes[] = {"NONE","DIFFERENCE","LINESEARCH","SNESNGMRESSelectType","SNES_NGMRES_SELECT_",0};

 10: PetscErrorCode SNESReset_NGMRES(SNES snes)
 11: {
 12:   SNES_NGMRES    *ngmres = (SNES_NGMRES*) snes->data;

 16:   VecDestroyVecs(ngmres->msize,&ngmres->Fdot);
 17:   VecDestroyVecs(ngmres->msize,&ngmres->Xdot);
 18:   SNESLineSearchDestroy(&ngmres->additive_linesearch);
 19:   return(0);
 20: }

 24: PetscErrorCode SNESDestroy_NGMRES(SNES snes)
 25: {
 27:   SNES_NGMRES    *ngmres = (SNES_NGMRES*)snes->data;

 30:   SNESReset_NGMRES(snes);
 31:   PetscFree5(ngmres->h,ngmres->beta,ngmres->xi,ngmres->fnorms,ngmres->q);
 32:   PetscFree(ngmres->s);
 33:   PetscFree(ngmres->xnorms);
 34: #if PETSC_USE_COMPLEX
 35:   PetscFree(ngmres->rwork);
 36: #endif
 37:   PetscFree(ngmres->work);
 38:   PetscFree(snes->data);
 39:   return(0);
 40: }

 44: PetscErrorCode SNESSetUp_NGMRES(SNES snes)
 45: {
 46:   SNES_NGMRES    *ngmres = (SNES_NGMRES*) snes->data;
 47:   const char     *optionsprefix;
 48:   PetscInt       msize,hsize;
 50:   DM             dm;

 53:   if (snes->pc && snes->pcside == PC_LEFT && snes->functype == SNES_FUNCTION_UNPRECONDITIONED) {
 54:     SETERRQ(PetscObjectComm((PetscObject)snes),PETSC_ERR_ARG_WRONGSTATE,"SNESNGMRES does not support left preconditioning with unpreconditioned function");
 55:   }
 56:   if (snes->pcside == PC_LEFT && snes->functype == SNES_FUNCTION_DEFAULT) snes->functype = SNES_FUNCTION_PRECONDITIONED;
 57:   SNESSetWorkVecs(snes,5);

 59:   if (!snes->vec_sol) {
 60:     SNESGetDM(snes,&dm);
 61:     DMCreateGlobalVector(dm,&snes->vec_sol);
 62:   }

 64:   if (!ngmres->Xdot) {VecDuplicateVecs(snes->vec_sol,ngmres->msize,&ngmres->Xdot);}
 65:   if (!ngmres->Fdot) {VecDuplicateVecs(snes->vec_sol,ngmres->msize,&ngmres->Fdot);}
 66:   if (!ngmres->setup_called) {
 67:     msize = ngmres->msize;          /* restart size */
 68:     hsize = msize * msize;

 70:     /* explicit least squares minimization solve */
 71:     PetscMalloc5(hsize,&ngmres->h, msize,&ngmres->beta, msize,&ngmres->xi, msize,&ngmres->fnorms, hsize,&ngmres->q);
 72:     PetscMalloc1(msize,&ngmres->xnorms);
 73:     ngmres->nrhs  = 1;
 74:     ngmres->lda   = msize;
 75:     ngmres->ldb   = msize;
 76:     PetscMalloc1(msize,&ngmres->s);
 77:     PetscMemzero(ngmres->h,   hsize*sizeof(PetscScalar));
 78:     PetscMemzero(ngmres->q,   hsize*sizeof(PetscScalar));
 79:     PetscMemzero(ngmres->xi,  msize*sizeof(PetscScalar));
 80:     PetscMemzero(ngmres->beta,msize*sizeof(PetscScalar));
 81:     ngmres->lwork = 12*msize;
 82: #if PETSC_USE_COMPLEX
 83:     PetscMalloc1(ngmres->lwork,&ngmres->rwork);
 84: #endif
 85:     PetscMalloc1(ngmres->lwork,&ngmres->work);
 86:   }

 88:   /* linesearch setup */
 89:   SNESGetOptionsPrefix(snes,&optionsprefix);

 91:   if (ngmres->select_type == SNES_NGMRES_SELECT_LINESEARCH) {
 92:     SNESLineSearchCreate(PetscObjectComm((PetscObject)snes),&ngmres->additive_linesearch);
 93:     SNESLineSearchSetSNES(ngmres->additive_linesearch,snes);
 94:     SNESLineSearchSetType(ngmres->additive_linesearch,SNESLINESEARCHL2);
 95:     SNESLineSearchAppendOptionsPrefix(ngmres->additive_linesearch,"additive_");
 96:     SNESLineSearchAppendOptionsPrefix(ngmres->additive_linesearch,optionsprefix);
 97:     SNESLineSearchSetFromOptions(ngmres->additive_linesearch);
 98:   }

100:   ngmres->setup_called = PETSC_TRUE;
101:   return(0);
102: }

106: PetscErrorCode SNESSetFromOptions_NGMRES(PetscOptions *PetscOptionsObject,SNES snes)
107: {
108:   SNES_NGMRES    *ngmres = (SNES_NGMRES*) snes->data;
110:   PetscBool      debug = PETSC_FALSE;
111:   SNESLineSearch linesearch;

114:   PetscOptionsHead(PetscOptionsObject,"SNES NGMRES options");
115:   PetscOptionsEnum("-snes_ngmres_select_type","Select type","SNESNGMRESSetSelectType",SNESNGMRESSelectTypes,
116:                           (PetscEnum)ngmres->select_type,(PetscEnum*)&ngmres->select_type,NULL);
117:   PetscOptionsEnum("-snes_ngmres_restart_type","Restart type","SNESNGMRESSetRestartType",SNESNGMRESRestartTypes,
118:                           (PetscEnum)ngmres->restart_type,(PetscEnum*)&ngmres->restart_type,NULL);
119:   PetscOptionsBool("-snes_ngmres_candidate", "Use candidate storage",              "SNES",ngmres->candidate,&ngmres->candidate,NULL);
120:   PetscOptionsBool("-snes_ngmres_approxfunc","Linearly approximate the function", "SNES",ngmres->approxfunc,&ngmres->approxfunc,NULL);
121:   PetscOptionsInt("-snes_ngmres_m",          "Number of directions",               "SNES",ngmres->msize,&ngmres->msize,NULL);
122:   PetscOptionsInt("-snes_ngmres_restart",    "Iterations before forced restart",   "SNES",ngmres->restart_periodic,&ngmres->restart_periodic,NULL);
123:   PetscOptionsInt("-snes_ngmres_restart_it", "Tolerance iterations before restart","SNES",ngmres->restart_it,&ngmres->restart_it,NULL);
124:   PetscOptionsBool("-snes_ngmres_monitor",   "Monitor actions of NGMRES",          "SNES",ngmres->monitor ? PETSC_TRUE : PETSC_FALSE,&debug,NULL);
125:   if (debug) {
126:     ngmres->monitor = PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes));
127:   }
128:   PetscOptionsReal("-snes_ngmres_gammaA",    "Residual selection constant",   "SNES",ngmres->gammaA,&ngmres->gammaA,NULL);
129:   PetscOptionsReal("-snes_ngmres_gammaC",    "Residual restart constant",     "SNES",ngmres->gammaC,&ngmres->gammaC,NULL);
130:   PetscOptionsReal("-snes_ngmres_epsilonB",  "Difference selection constant", "SNES",ngmres->epsilonB,&ngmres->epsilonB,NULL);
131:   PetscOptionsReal("-snes_ngmres_deltaB",    "Difference residual selection constant", "SNES",ngmres->deltaB,&ngmres->deltaB,NULL);
132:   PetscOptionsBool("-snes_ngmres_single_reduction", "Aggregate reductions",  "SNES",ngmres->singlereduction,&ngmres->singlereduction,NULL);
133:   PetscOptionsTail();
134:   if ((ngmres->gammaA > ngmres->gammaC) && (ngmres->gammaC > 2.)) ngmres->gammaC = ngmres->gammaA;

136:   /* set the default type of the line search if the user hasn't already. */
137:   if (!snes->linesearch) {
138:     SNESGetLineSearch(snes,&linesearch);
139:     SNESLineSearchSetType(linesearch,SNESLINESEARCHBASIC);
140:   }
141:   return(0);
142: }

146: PetscErrorCode SNESView_NGMRES(SNES snes,PetscViewer viewer)
147: {
148:   SNES_NGMRES    *ngmres = (SNES_NGMRES*) snes->data;
149:   PetscBool      iascii;

153:   PetscObjectTypeCompare((PetscObject) viewer,PETSCVIEWERASCII,&iascii);
154:   if (iascii) {
155:     PetscViewerASCIIPrintf(viewer,"  Number of stored past updates: %d\n", ngmres->msize);
156:     PetscViewerASCIIPrintf(viewer,"  Residual selection: gammaA=%1.0e, gammaC=%1.0e\n",ngmres->gammaA,ngmres->gammaC);
157:     PetscViewerASCIIPrintf(viewer,"  Difference restart: epsilonB=%1.0e, deltaB=%1.0e\n",ngmres->epsilonB,ngmres->deltaB);
158:   }
159:   return(0);
160: }

164: PetscErrorCode SNESSolve_NGMRES(SNES snes)
165: {
166:   SNES_NGMRES          *ngmres = (SNES_NGMRES*) snes->data;
167:   /* present solution, residual, and preconditioned residual */
168:   Vec                  X,F,B,D,Y;

170:   /* candidate linear combination answers */
171:   Vec                  XA,FA,XM,FM;

173:   /* coefficients and RHS to the minimization problem */
174:   PetscReal            fnorm,fMnorm,fAnorm;
175:   PetscReal            xnorm,xMnorm,xAnorm;
176:   PetscReal            ynorm,yMnorm,yAnorm;
177:   PetscInt             k,k_restart,l,ivec,restart_count = 0;

179:   /* solution selection data */
180:   PetscBool            selectRestart;
181:   PetscReal            dnorm,dminnorm = 0.0;
182:   PetscReal            fminnorm;

184:   SNESConvergedReason  reason;
185:   SNESLineSearchReason lssucceed;
186:   PetscErrorCode       ierr;


190:   if (snes->xl || snes->xu || snes->ops->computevariablebounds) {
191:     SETERRQ1(PetscObjectComm((PetscObject)snes),PETSC_ERR_ARG_WRONGSTATE, "SNES solver %s does not support bounds", ((PetscObject)snes)->type_name);
192:   }

194:   PetscCitationsRegister(SNESCitation,&SNEScite);
195:   /* variable initialization */
196:   snes->reason = SNES_CONVERGED_ITERATING;
197:   X            = snes->vec_sol;
198:   F            = snes->vec_func;
199:   B            = snes->vec_rhs;
200:   XA           = snes->vec_sol_update;
201:   FA           = snes->work[0];
202:   D            = snes->work[1];

204:   /* work for the line search */
205:   Y  = snes->work[2];
206:   XM = snes->work[3];
207:   FM = snes->work[4];

209:   PetscObjectSAWsTakeAccess((PetscObject)snes);
210:   snes->iter = 0;
211:   snes->norm = 0.;
212:   PetscObjectSAWsGrantAccess((PetscObject)snes);

214:   /* initialization */

216:   if (snes->pc && snes->pcside == PC_LEFT) {
217:     SNESApplyNPC(snes,X,NULL,F);
218:     SNESGetConvergedReason(snes->pc,&reason);
219:     if (reason < 0  && reason != SNES_DIVERGED_MAX_IT) {
220:       snes->reason = SNES_DIVERGED_INNER;
221:       return(0);
222:     }
223:     VecNorm(F,NORM_2,&fnorm);
224:   } else {
225:     if (!snes->vec_func_init_set) {
226:       SNESComputeFunction(snes,X,F);
227:     } else snes->vec_func_init_set = PETSC_FALSE;

229:     VecNorm(F,NORM_2,&fnorm);
230:     SNESCheckFunctionNorm(snes,fnorm);
231:   }
232:   fminnorm = fnorm;

234:   PetscObjectSAWsTakeAccess((PetscObject)snes);
235:   snes->norm = fnorm;
236:   PetscObjectSAWsGrantAccess((PetscObject)snes);
237:   SNESLogConvergenceHistory(snes,fnorm,0);
238:   SNESMonitor(snes,0,fnorm);
239:   (*snes->ops->converged)(snes,0,0.0,0.0,fnorm,&snes->reason,snes->cnvP);
240:   if (snes->reason) return(0);
241:   SNESNGMRESUpdateSubspace_Private(snes,0,0,F,fnorm,X);

243:   k_restart = 1;
244:   l         = 1;
245:   ivec      = 0;
246:   for (k=1; k < snes->max_its+1; k++) {
247:     /* Computation of x^M */
248:     if (snes->pc && snes->pcside == PC_RIGHT) {
249:       VecCopy(X,XM);
250:       SNESSetInitialFunction(snes->pc,F);

252:       PetscLogEventBegin(SNES_NPCSolve,snes->pc,XM,B,0);
253:       SNESSolve(snes->pc,B,XM);
254:       PetscLogEventEnd(SNES_NPCSolve,snes->pc,XM,B,0);

256:       SNESGetConvergedReason(snes->pc,&reason);
257:       if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
258:         snes->reason = SNES_DIVERGED_INNER;
259:         return(0);
260:       }
261:       SNESGetNPCFunction(snes,FM,&fMnorm);
262:     } else {
263:       /* no preconditioner -- just take gradient descent with line search */
264:       VecCopy(F,Y);
265:       VecCopy(F,FM);
266:       VecCopy(X,XM);

268:       fMnorm = fnorm;

270:       SNESLineSearchApply(snes->linesearch,XM,FM,&fMnorm,Y);
271:       SNESLineSearchGetReason(snes->linesearch,&lssucceed);
272:       if (lssucceed) {
273:         if (++snes->numFailures >= snes->maxFailures) {
274:           snes->reason = SNES_DIVERGED_LINE_SEARCH;
275:           return(0);
276:         }
277:       }
278:     }
279:     SNESNGMRESFormCombinedSolution_Private(snes,ivec,l,XM,FM,fMnorm,X,XA,FA);
280:     /* r = F(x) */
281:     if (fminnorm > fMnorm) fminnorm = fMnorm;  /* the minimum norm is now of F^M */

283:     /* differences for selection and restart */
284:     if (ngmres->restart_type == SNES_NGMRES_RESTART_DIFFERENCE || ngmres->select_type == SNES_NGMRES_SELECT_DIFFERENCE) {
285:       SNESNGMRESNorms_Private(snes,l,X,F,XM,FM,XA,FA,D,&dnorm,&dminnorm,&xMnorm,NULL,&yMnorm,&xAnorm,&fAnorm,&yAnorm);
286:     } else {
287:       SNESNGMRESNorms_Private(snes,l,X,F,XM,FM,XA,FA,D,NULL,NULL,&xMnorm,NULL,&yMnorm,&xAnorm,&fAnorm,&yAnorm);
288:     }
289:     SNESCheckFunctionNorm(snes,fnorm);

291:     /* combination (additive) or selection (multiplicative) of the N-GMRES solution */
292:     SNESNGMRESSelect_Private(snes,k_restart,XM,FM,xMnorm,fMnorm,yMnorm,XA,FA,xAnorm,fAnorm,yAnorm,dnorm,fminnorm,dminnorm,X,F,Y,&xnorm,&fnorm,&ynorm);
293:     selectRestart = PETSC_FALSE;
294:     if (ngmres->restart_type == SNES_NGMRES_RESTART_DIFFERENCE) {
295:       SNESNGMRESSelectRestart_Private(snes,l,fAnorm,dnorm,fminnorm,dminnorm,&selectRestart);
296:       /* if the restart conditions persist for more than restart_it iterations, restart. */
297:       if (selectRestart) restart_count++;
298:       else restart_count = 0;
299:     } else if (ngmres->restart_type == SNES_NGMRES_RESTART_PERIODIC) {
300:       if (k_restart > ngmres->restart_periodic) {
301:         if (ngmres->monitor) PetscViewerASCIIPrintf(ngmres->monitor,"periodic restart after %D iterations\n",k_restart);
302:         restart_count = ngmres->restart_it;
303:       }
304:     }
305:     ivec = k_restart % ngmres->msize; /* replace the last used part of the subspace */
306:     /* restart after restart conditions have persisted for a fixed number of iterations */
307:     if (restart_count >= ngmres->restart_it) {
308:       if (ngmres->monitor) {
309:         PetscViewerASCIIPrintf(ngmres->monitor,"Restarted at iteration %d\n",k_restart);
310:       }
311:       restart_count = 0;
312:       k_restart     = 1;
313:       l             = 1;
314:       ivec          = 0;
315:       /* q_{00} = nu */
316:       SNESNGMRESUpdateSubspace_Private(snes,0,0,FM,fMnorm,XM);
317:     } else {
318:       /* select the current size of the subspace */
319:       if (l < ngmres->msize) l++;
320:       k_restart++;
321:       /* place the current entry in the list of previous entries */
322:       if (ngmres->candidate) {
323:         if (fminnorm > fMnorm) fminnorm = fMnorm;
324:         SNESNGMRESUpdateSubspace_Private(snes,ivec,l,FM,fMnorm,XM);
325:       } else {
326:         if (fminnorm > fnorm) fminnorm = fnorm;
327:         SNESNGMRESUpdateSubspace_Private(snes,ivec,l,F,fnorm,X);
328:       }
329:     }

331:     PetscObjectSAWsTakeAccess((PetscObject)snes);
332:     snes->iter = k;
333:     snes->norm = fnorm;
334:     PetscObjectSAWsGrantAccess((PetscObject)snes);
335:     SNESLogConvergenceHistory(snes,snes->norm,snes->iter);
336:     SNESMonitor(snes,snes->iter,snes->norm);
337:     (*snes->ops->converged)(snes,snes->iter,0,0,fnorm,&snes->reason,snes->cnvP);
338:     if (snes->reason) return(0);
339:   }
340:   snes->reason = SNES_DIVERGED_MAX_IT;
341:   return(0);
342: }

346: /*@
347:     SNESNGMRESSetRestartType - Sets the restart type for SNESNGMRES.

349:     Logically Collective on SNES

351:     Input Parameters:
352: +   snes - the iterative context
353: -   rtype - restart type

355:     Options Database:
356: +   -snes_ngmres_restart_type<difference,periodic,none> - set the restart type
357: -   -snes_ngmres_restart[30] - sets the number of iterations before restart for periodic

359:     Level: intermediate

361:     SNESNGMRESRestartTypes:
362: +   SNES_NGMRES_RESTART_NONE - never restart
363: .   SNES_NGMRES_RESTART_DIFFERENCE - restart based upon difference criteria
364: -   SNES_NGMRES_RESTART_PERIODIC - restart after a fixed number of iterations

366:     Notes:
367:     The default line search used is the L2 line search and it requires two additional function evaluations.

369: .keywords: SNES, SNESNGMRES, restart, type, set SNESLineSearch
370: @*/
371: PetscErrorCode SNESNGMRESSetRestartType(SNES snes,SNESNGMRESRestartType rtype)
372: {

377:   PetscTryMethod(snes,"SNESNGMRESSetRestartType_C",(SNES,SNESNGMRESRestartType),(snes,rtype));
378:   return(0);
379: }

383: /*@
384:     SNESNGMRESSetSelectType - Sets the selection type for SNESNGMRES.  This determines how the candidate solution and
385:     combined solution are used to create the next iterate.

387:     Logically Collective on SNES

389:     Input Parameters:
390: +   snes - the iterative context
391: -   stype - selection type

393:     Options Database:
394: .   -snes_ngmres_select_type<difference,none,linesearch>

396:     Level: intermediate

398:     SNESNGMRESSelectTypes:
399: +   SNES_NGMRES_SELECT_NONE - choose the combined solution all the time
400: .   SNES_NGMRES_SELECT_DIFFERENCE - choose based upon the selection criteria
401: -   SNES_NGMRES_SELECT_LINESEARCH - choose based upon line search combination

403:     Notes:
404:     The default line search used is the L2 line search and it requires two additional function evaluations.

406: .keywords: SNES, SNESNGMRES, selection, type, set SNESLineSearch
407: @*/
408: PetscErrorCode SNESNGMRESSetSelectType(SNES snes,SNESNGMRESSelectType stype)
409: {

414:   PetscTryMethod(snes,"SNESNGMRESSetSelectType_C",(SNES,SNESNGMRESSelectType),(snes,stype));
415:   return(0);
416: }

420: PetscErrorCode SNESNGMRESSetSelectType_NGMRES(SNES snes,SNESNGMRESSelectType stype)
421: {
422:   SNES_NGMRES *ngmres = (SNES_NGMRES*)snes->data;

425:   ngmres->select_type = stype;
426:   return(0);
427: }

431: PetscErrorCode SNESNGMRESSetRestartType_NGMRES(SNES snes,SNESNGMRESRestartType rtype)
432: {
433:   SNES_NGMRES *ngmres = (SNES_NGMRES*)snes->data;

436:   ngmres->restart_type = rtype;
437:   return(0);
438: }

440: /*MC
441:   SNESNGMRES - The Nonlinear Generalized Minimum Residual method.

443:    Level: beginner

445:    Options Database:
446: +  -snes_ngmres_select_type<difference,none,linesearch> - choose the select between candidate and combined solution
447: .  -snes_ngmres_restart_type<difference,none,periodic> - choose the restart conditions
448: .  -snes_ngmres_candidate        - Use NGMRES variant which combines candidate solutions instead of actual solutions
449: .  -snes_ngmres_m                - Number of stored previous solutions and residuals
450: .  -snes_ngmres_restart_it       - Number of iterations the restart conditions hold before restart
451: .  -snes_ngmres_gammaA           - Residual tolerance for solution select between the candidate and combination
452: .  -snes_ngmres_gammaC           - Residual tolerance for restart
453: .  -snes_ngmres_epsilonB         - Difference tolerance between subsequent solutions triggering restart
454: .  -snes_ngmres_deltaB           - Difference tolerance between residuals triggering restart
455: .  -snes_ngmres_monitor          - Prints relevant information about the ngmres iteration
456: .  -snes_linesearch_type <basic,l2,cp> - Line search type used for the default smoother
457: -  -additive_snes_linesearch_type - linesearch type used to select between the candidate and combined solution with additive select type

459:    Notes:

461:    The N-GMRES method combines m previous solutions into a minimum-residual solution by solving a small linearized
462:    optimization problem at each iteration.

464:    References:

466:    "Krylov Subspace Acceleration of Nonlinear Multigrid with Application to Recirculating Flows", C. W. Oosterlee and T. Washio,
467:    SIAM Journal on Scientific Computing, 21(5), 2000.

469: .seealso: SNESCreate(), SNES, SNESSetType(), SNESType (for list of available types)
470: M*/

474: PETSC_EXTERN PetscErrorCode SNESCreate_NGMRES(SNES snes)
475: {
476:   SNES_NGMRES    *ngmres;

480:   snes->ops->destroy        = SNESDestroy_NGMRES;
481:   snes->ops->setup          = SNESSetUp_NGMRES;
482:   snes->ops->setfromoptions = SNESSetFromOptions_NGMRES;
483:   snes->ops->view           = SNESView_NGMRES;
484:   snes->ops->solve          = SNESSolve_NGMRES;
485:   snes->ops->reset          = SNESReset_NGMRES;

487:   snes->usespc   = PETSC_TRUE;
488:   snes->usesksp  = PETSC_FALSE;
489:   snes->pcside   = PC_RIGHT;

491:   PetscNewLog(snes,&ngmres);
492:   snes->data    = (void*) ngmres;
493:   ngmres->msize = 30;

495:   if (!snes->tolerancesset) {
496:     snes->max_funcs = 30000;
497:     snes->max_its   = 10000;
498:   }

500:   ngmres->candidate = PETSC_FALSE;

502:   ngmres->additive_linesearch = NULL;
503:   ngmres->approxfunc       = PETSC_FALSE;
504:   ngmres->restart_it       = 2;
505:   ngmres->restart_periodic = 30;
506:   ngmres->gammaA           = 2.0;
507:   ngmres->gammaC           = 2.0;
508:   ngmres->deltaB           = 0.9;
509:   ngmres->epsilonB         = 0.1;

511:   ngmres->restart_type = SNES_NGMRES_RESTART_DIFFERENCE;
512:   ngmres->select_type  = SNES_NGMRES_SELECT_DIFFERENCE;

514:   PetscObjectComposeFunction((PetscObject)snes,"SNESNGMRESSetSelectType_C",SNESNGMRESSetSelectType_NGMRES);
515:   PetscObjectComposeFunction((PetscObject)snes,"SNESNGMRESSetRestartType_C",SNESNGMRESSetRestartType_NGMRES);
516:   return(0);
517: }