Actual source code: snesncg.c

  1: #include <../src/snes/impls/ncg/snesncgimpl.h>
  2: const char *const SNESNCGTypes[] = {"FR", "PRP", "HS", "DY", "CD", "SNESNCGType", "SNES_NCG_", NULL};

  4: static PetscErrorCode SNESReset_NCG(SNES snes)
  5: {
  6:   PetscFunctionBegin;
  7:   PetscFunctionReturn(PETSC_SUCCESS);
  8: }

 10: /*
 11:   SNESDestroy_NCG - Destroys the private SNES_NCG context that was created with SNESCreate_NCG().

 13:   Input Parameter:
 14: . snes - the SNES context

 16:   Application Interface Routine: SNESDestroy()
 17: */
 18: static PetscErrorCode SNESDestroy_NCG(SNES snes)
 19: {
 20:   PetscFunctionBegin;
 21:   PetscCall(PetscObjectComposeFunction((PetscObject)snes, "SNESNCGSetType_C", NULL));
 22:   PetscCall(PetscFree(snes->data));
 23:   PetscFunctionReturn(PETSC_SUCCESS);
 24: }

 26: /*
 27:    SNESSetUp_NCG - Sets up the internal data structures for the later use
 28:    of the SNESNCG nonlinear solver.

 30:    Input Parameters:
 31: +  snes - the SNES context
 32: -  x - the solution vector

 34:    Application Interface Routine: SNESSetUp()
 35:  */

 37: static PetscErrorCode SNESSetUp_NCG(SNES snes)
 38: {
 39:   PetscFunctionBegin;
 40:   PetscCall(SNESSetWorkVecs(snes, 2));
 41:   PetscCheck(snes->npcside != PC_RIGHT, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_WRONGSTATE, "SNESNCG only supports left preconditioning");
 42:   if (snes->functype == SNES_FUNCTION_DEFAULT) snes->functype = SNES_FUNCTION_UNPRECONDITIONED;
 43:   PetscFunctionReturn(PETSC_SUCCESS);
 44: }

 46: static PetscErrorCode SNESLineSearchApply_NCGLinear(SNESLineSearch linesearch)
 47: {
 48:   PetscScalar alpha, ptAp;
 49:   Vec         X, Y, F, W;
 50:   SNES        snes;
 51:   PetscReal  *fnorm, *xnorm, *ynorm;

 53:   PetscFunctionBegin;
 54:   PetscCall(SNESLineSearchGetSNES(linesearch, &snes));
 55:   X     = linesearch->vec_sol;
 56:   W     = linesearch->vec_sol_new;
 57:   F     = linesearch->vec_func;
 58:   Y     = linesearch->vec_update;
 59:   fnorm = &linesearch->fnorm;
 60:   xnorm = &linesearch->xnorm;
 61:   ynorm = &linesearch->ynorm;

 63:   if (!snes->jacobian) PetscCall(SNESSetUpMatrices(snes));

 65:   /*

 67:    The exact step size for unpreconditioned linear CG is just:
 68:    alpha = (r, r) / (p, Ap) = (f, f) / (y, Jy)
 69:    */
 70:   PetscCall(SNESComputeJacobian(snes, X, snes->jacobian, snes->jacobian_pre));
 71:   PetscCall(VecDot(F, F, &alpha));
 72:   PetscCall(MatMult(snes->jacobian, Y, W));
 73:   PetscCall(VecDot(Y, W, &ptAp));
 74:   alpha = alpha / ptAp;
 75:   PetscCall(VecAXPY(X, -alpha, Y));
 76:   PetscCall(SNESComputeFunction(snes, X, F));

 78:   PetscCall(VecNorm(F, NORM_2, fnorm));
 79:   PetscCall(VecNorm(X, NORM_2, xnorm));
 80:   PetscCall(VecNorm(Y, NORM_2, ynorm));
 81:   PetscFunctionReturn(PETSC_SUCCESS);
 82: }

 84: /*MC
 85:    SNESLINESEARCHNCGLINEAR - Special line search only for the nonlinear CG solver `SNESNCG`

 87:    This line search uses the length "as if" the problem is linear (that is what is computed by the linear CG method) using the Jacobian of the function.
 88:    alpha = (r, r) / (p, Ap) = (f, f) / (y, Jy) where r (f) is the current residual (function value), p (y) is the current search direction.

 90:    Notes:
 91:    This requires a Jacobian-vector product but does not require the solution of a linear system with the Jacobian

 93:    This is a "odd-ball" line search, we don't know if it is in the literature or used in practice by anyone.

 95:    Level: advanced

 97: .seealso: `SNESLineSearchCreate()`, `SNESLineSearchSetType()`
 98: M*/

100: PETSC_EXTERN PetscErrorCode SNESLineSearchCreate_NCGLinear(SNESLineSearch linesearch)
101: {
102:   PetscFunctionBegin;
103:   linesearch->ops->apply          = SNESLineSearchApply_NCGLinear;
104:   linesearch->ops->destroy        = NULL;
105:   linesearch->ops->setfromoptions = NULL;
106:   linesearch->ops->reset          = NULL;
107:   linesearch->ops->view           = NULL;
108:   linesearch->ops->setup          = NULL;
109:   PetscFunctionReturn(PETSC_SUCCESS);
110: }

112: /*
113:   SNESSetFromOptions_NCG - Sets various parameters for the SNESNCG method.

115:   Input Parameter:
116: . snes - the SNES context

118:   Application Interface Routine: SNESSetFromOptions()
119: */
120: static PetscErrorCode SNESSetFromOptions_NCG(SNES snes, PetscOptionItems *PetscOptionsObject)
121: {
122:   SNES_NCG      *ncg     = (SNES_NCG *)snes->data;
123:   PetscBool      debug   = PETSC_FALSE;
124:   SNESNCGType    ncgtype = ncg->type;
125:   SNESLineSearch linesearch;

127:   PetscFunctionBegin;
128:   PetscOptionsHeadBegin(PetscOptionsObject, "SNES NCG options");
129:   PetscCall(PetscOptionsBool("-snes_ncg_monitor", "Monitor the beta values used in the NCG iterations", "SNES", ncg->monitor ? PETSC_TRUE : PETSC_FALSE, &debug, NULL));
130:   if (debug) ncg->monitor = PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes));
131:   PetscCall(PetscOptionsEnum("-snes_ncg_type", "NCG Beta type used", "SNESNCGSetType", SNESNCGTypes, (PetscEnum)ncg->type, (PetscEnum *)&ncgtype, NULL));
132:   PetscCall(SNESNCGSetType(snes, ncgtype));
133:   PetscOptionsHeadEnd();
134:   if (!snes->linesearch) {
135:     PetscCall(SNESGetLineSearch(snes, &linesearch));
136:     if (!((PetscObject)linesearch)->type_name) {
137:       if (!snes->npc) {
138:         PetscCall(SNESLineSearchSetType(linesearch, SNESLINESEARCHCP));
139:       } else {
140:         PetscCall(SNESLineSearchSetType(linesearch, SNESLINESEARCHL2));
141:       }
142:     }
143:   }
144:   PetscFunctionReturn(PETSC_SUCCESS);
145: }

147: /*
148:   SNESView_NCG - Prints info from the SNESNCG data structure.

150:   Input Parameters:
151: + SNES - the SNES context
152: - viewer - visualization context

154:   Application Interface Routine: SNESView()
155: */
156: static PetscErrorCode SNESView_NCG(SNES snes, PetscViewer viewer)
157: {
158:   SNES_NCG *ncg = (SNES_NCG *)snes->data;
159:   PetscBool iascii;

161:   PetscFunctionBegin;
162:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &iascii));
163:   if (iascii) PetscCall(PetscViewerASCIIPrintf(viewer, "  type: %s\n", SNESNCGTypes[ncg->type]));
164:   PetscFunctionReturn(PETSC_SUCCESS);
165: }

167: /*

169:  Assuming F = SNESComputeFunction(X) compute Y^tJ^tF using a simple secant approximation of the jacobian.

171:  This routine is not currently used. I don't know what its intended purpose is.

173:  Note it has a hardwired differencing parameter of 1e-5

175:  */
176: PetscErrorCode SNESNCGComputeYtJtF_Private(SNES snes, Vec X, Vec F, Vec Y, Vec W, Vec G, PetscScalar *ytJtf)
177: {
178:   PetscScalar ftf, ftg, fty, h;

180:   PetscFunctionBegin;
181:   PetscCall(VecDot(F, F, &ftf));
182:   PetscCall(VecDot(F, Y, &fty));
183:   h = 1e-5 * fty / fty;
184:   PetscCall(VecCopy(X, W));
185:   PetscCall(VecAXPY(W, -h, Y)); /* this is arbitrary */
186:   PetscCall(SNESComputeFunction(snes, W, G));
187:   PetscCall(VecDot(G, F, &ftg));
188:   *ytJtf = (ftg - ftf) / h;
189:   PetscFunctionReturn(PETSC_SUCCESS);
190: }

192: /*@
193:     SNESNCGSetType - Sets the conjugate update type for nonlinear CG `SNESNCG`.

195:     Logically Collective

197:     Input Parameters:
198: +   snes - the iterative context
199: -   btype - update type

201:     Options Database Key:
202: .   -snes_ncg_type <prp,fr,hs,dy,cd> -strategy for selecting algorithm for computing beta

204:     Level: intermediate

206:     `SNESNCGType`s:
207: +   `SNES_NCG_FR` - Fletcher-Reeves update
208: .   `SNES_NCG_PRP` - Polak-Ribiere-Polyak update
209: .   `SNES_NCG_HS` - Hestenes-Steifel update
210: .   `SNES_NCG_DY` - Dai-Yuan update
211: -   `SNES_NCG_CD` - Conjugate Descent update

213:    Notes:
214:    `SNES_NCG_PRP` is the default, and the only one that tolerates generalized search directions.

216:    It is not clear what "generalized search directions" means, does it mean use with a nonlinear preconditioner,
217:    that is using -npc_snes_type <type>, `SNESSetNPC()`, or `SNESGetNPC()`?

219:    Developer Note:
220:    There should be a `SNESNCGSetType()`

222: .seealso: `SNESNCGType`, `SNES_NCG_FR`, `SNES_NCG_PRP`, `SNES_NCG_HS`, `SNES_NCG_DY`, `SNES_NCG_CD`
223: @*/
224: PetscErrorCode SNESNCGSetType(SNES snes, SNESNCGType btype)
225: {
226:   PetscFunctionBegin;
228:   PetscTryMethod(snes, "SNESNCGSetType_C", (SNES, SNESNCGType), (snes, btype));
229:   PetscFunctionReturn(PETSC_SUCCESS);
230: }

232: static PetscErrorCode SNESNCGSetType_NCG(SNES snes, SNESNCGType btype)
233: {
234:   SNES_NCG *ncg = (SNES_NCG *)snes->data;

236:   PetscFunctionBegin;
237:   ncg->type = btype;
238:   PetscFunctionReturn(PETSC_SUCCESS);
239: }

241: /*
242:   SNESSolve_NCG - Solves a nonlinear system with the Nonlinear Conjugate Gradient method.

244:   Input Parameters:
245: . snes - the SNES context

247:   Output Parameter:
248: . outits - number of iterations until termination

250:   Application Interface Routine: SNESSolve()
251: */
252: static PetscErrorCode SNESSolve_NCG(SNES snes)
253: {
254:   SNES_NCG            *ncg = (SNES_NCG *)snes->data;
255:   Vec                  X, dX, lX, F, dXold;
256:   PetscReal            fnorm, ynorm, xnorm, beta = 0.0;
257:   PetscScalar          dXdotdX, dXolddotdXold, dXdotdXold, lXdotdX, lXdotdXold;
258:   PetscInt             maxits, i;
259:   SNESLineSearchReason lsresult = SNES_LINESEARCH_SUCCEEDED;
260:   SNESLineSearch       linesearch;
261:   SNESConvergedReason  reason;

263:   PetscFunctionBegin;
264:   PetscCheck(!snes->xl && !snes->xu && !snes->ops->computevariablebounds, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_WRONGSTATE, "SNES solver %s does not support bounds", ((PetscObject)snes)->type_name);

266:   PetscCall(PetscCitationsRegister(SNESCitation, &SNEScite));
267:   snes->reason = SNES_CONVERGED_ITERATING;

269:   maxits = snes->max_its;        /* maximum number of iterations */
270:   X      = snes->vec_sol;        /* X^n */
271:   dXold  = snes->work[0];        /* The previous iterate of X */
272:   dX     = snes->work[1];        /* the preconditioned direction */
273:   lX     = snes->vec_sol_update; /* the conjugate direction */
274:   F      = snes->vec_func;       /* residual vector */

276:   PetscCall(SNESGetLineSearch(snes, &linesearch));

278:   PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
279:   snes->iter = 0;
280:   snes->norm = 0.;
281:   PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));

283:   /* compute the initial function and preconditioned update dX */

285:   if (snes->npc && snes->functype == SNES_FUNCTION_PRECONDITIONED) {
286:     PetscCall(SNESApplyNPC(snes, X, NULL, dX));
287:     PetscCall(SNESGetConvergedReason(snes->npc, &reason));
288:     if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
289:       snes->reason = SNES_DIVERGED_INNER;
290:       PetscFunctionReturn(PETSC_SUCCESS);
291:     }
292:     PetscCall(VecCopy(dX, F));
293:     PetscCall(VecNorm(F, NORM_2, &fnorm));
294:   } else {
295:     if (!snes->vec_func_init_set) {
296:       PetscCall(SNESComputeFunction(snes, X, F));
297:     } else snes->vec_func_init_set = PETSC_FALSE;

299:     /* convergence test */
300:     PetscCall(VecNorm(F, NORM_2, &fnorm));
301:     SNESCheckFunctionNorm(snes, fnorm);
302:     PetscCall(VecCopy(F, dX));
303:   }
304:   if (snes->npc) {
305:     if (snes->functype == SNES_FUNCTION_UNPRECONDITIONED) {
306:       PetscCall(SNESApplyNPC(snes, X, F, dX));
307:       PetscCall(SNESGetConvergedReason(snes->npc, &reason));
308:       if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
309:         snes->reason = SNES_DIVERGED_INNER;
310:         PetscFunctionReturn(PETSC_SUCCESS);
311:       }
312:     }
313:   }
314:   PetscCall(VecCopy(dX, lX));
315:   PetscCall(VecDot(dX, dX, &dXdotdX));

317:   PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
318:   snes->norm = fnorm;
319:   PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
320:   PetscCall(SNESLogConvergenceHistory(snes, fnorm, 0));
321:   PetscCall(SNESMonitor(snes, 0, fnorm));

323:   /* test convergence */
324:   PetscUseTypeMethod(snes, converged, 0, 0.0, 0.0, fnorm, &snes->reason, snes->cnvP);
325:   if (snes->reason) PetscFunctionReturn(PETSC_SUCCESS);

327:   /* Call general purpose update function */
328:   PetscTryTypeMethod(snes, update, snes->iter);

330:   /* first update -- just use the (preconditioned) residual direction for the initial conjugate direction */

332:   for (i = 1; i < maxits + 1; i++) {
333:     /* some update types require the old update direction or conjugate direction */
334:     if (ncg->type != SNES_NCG_FR) PetscCall(VecCopy(dX, dXold));
335:     PetscCall(SNESLineSearchApply(linesearch, X, F, &fnorm, lX));
336:     PetscCall(SNESLineSearchGetReason(linesearch, &lsresult));
337:     PetscCall(SNESLineSearchGetNorms(linesearch, &xnorm, &fnorm, &ynorm));
338:     if (lsresult) {
339:       if (++snes->numFailures >= snes->maxFailures) {
340:         snes->reason = SNES_DIVERGED_LINE_SEARCH;
341:         PetscFunctionReturn(PETSC_SUCCESS);
342:       }
343:     }
344:     if (snes->nfuncs >= snes->max_funcs && snes->max_funcs >= 0) {
345:       snes->reason = SNES_DIVERGED_FUNCTION_COUNT;
346:       PetscFunctionReturn(PETSC_SUCCESS);
347:     }
348:     /* Monitor convergence */
349:     PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
350:     snes->iter  = i;
351:     snes->norm  = fnorm;
352:     snes->xnorm = xnorm;
353:     snes->ynorm = ynorm;
354:     PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
355:     PetscCall(SNESLogConvergenceHistory(snes, snes->norm, 0));
356:     PetscCall(SNESMonitor(snes, snes->iter, snes->norm));

358:     /* Test for convergence */
359:     PetscUseTypeMethod(snes, converged, snes->iter, xnorm, ynorm, fnorm, &snes->reason, snes->cnvP);
360:     if (snes->reason) PetscFunctionReturn(PETSC_SUCCESS);

362:     /* Call general purpose update function */
363:     PetscTryTypeMethod(snes, update, snes->iter);
364:     if (snes->npc) {
365:       if (snes->functype == SNES_FUNCTION_PRECONDITIONED) {
366:         PetscCall(SNESApplyNPC(snes, X, NULL, dX));
367:         PetscCall(SNESGetConvergedReason(snes->npc, &reason));
368:         if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
369:           snes->reason = SNES_DIVERGED_INNER;
370:           PetscFunctionReturn(PETSC_SUCCESS);
371:         }
372:         PetscCall(VecCopy(dX, F));
373:       } else {
374:         PetscCall(SNESApplyNPC(snes, X, F, dX));
375:         PetscCall(SNESGetConvergedReason(snes->npc, &reason));
376:         if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
377:           snes->reason = SNES_DIVERGED_INNER;
378:           PetscFunctionReturn(PETSC_SUCCESS);
379:         }
380:       }
381:     } else {
382:       PetscCall(VecCopy(F, dX));
383:     }

385:     /* compute the conjugate direction lX = dX + beta*lX with beta = ((dX, dX) / (dX_old, dX_old) (Fletcher-Reeves update)*/
386:     switch (ncg->type) {
387:     case SNES_NCG_FR: /* Fletcher-Reeves */
388:       dXolddotdXold = dXdotdX;
389:       PetscCall(VecDot(dX, dX, &dXdotdX));
390:       beta = PetscRealPart(dXdotdX / dXolddotdXold);
391:       break;
392:     case SNES_NCG_PRP: /* Polak-Ribiere-Poylak */
393:       dXolddotdXold = dXdotdX;
394:       PetscCall(VecDotBegin(dX, dX, &dXdotdXold));
395:       PetscCall(VecDotBegin(dXold, dX, &dXdotdXold));
396:       PetscCall(VecDotEnd(dX, dX, &dXdotdX));
397:       PetscCall(VecDotEnd(dXold, dX, &dXdotdXold));
398:       beta = PetscRealPart(((dXdotdX - dXdotdXold) / dXolddotdXold));
399:       if (beta < 0.0) beta = 0.0; /* restart */
400:       break;
401:     case SNES_NCG_HS: /* Hestenes-Stiefel */
402:       PetscCall(VecDotBegin(dX, dX, &dXdotdX));
403:       PetscCall(VecDotBegin(dX, dXold, &dXdotdXold));
404:       PetscCall(VecDotBegin(lX, dX, &lXdotdX));
405:       PetscCall(VecDotBegin(lX, dXold, &lXdotdXold));
406:       PetscCall(VecDotEnd(dX, dX, &dXdotdX));
407:       PetscCall(VecDotEnd(dX, dXold, &dXdotdXold));
408:       PetscCall(VecDotEnd(lX, dX, &lXdotdX));
409:       PetscCall(VecDotEnd(lX, dXold, &lXdotdXold));
410:       beta = PetscRealPart((dXdotdX - dXdotdXold) / (lXdotdX - lXdotdXold));
411:       break;
412:     case SNES_NCG_DY: /* Dai-Yuan */
413:       PetscCall(VecDotBegin(dX, dX, &dXdotdX));
414:       PetscCall(VecDotBegin(lX, dX, &lXdotdX));
415:       PetscCall(VecDotBegin(lX, dXold, &lXdotdXold));
416:       PetscCall(VecDotEnd(dX, dX, &dXdotdX));
417:       PetscCall(VecDotEnd(lX, dX, &lXdotdX));
418:       PetscCall(VecDotEnd(lX, dXold, &lXdotdXold));
419:       beta = PetscRealPart(dXdotdX / (lXdotdXold - lXdotdX));
420:       break;
421:     case SNES_NCG_CD: /* Conjugate Descent */
422:       PetscCall(VecDotBegin(dX, dX, &dXdotdX));
423:       PetscCall(VecDotBegin(lX, dXold, &lXdotdXold));
424:       PetscCall(VecDotEnd(dX, dX, &dXdotdX));
425:       PetscCall(VecDotEnd(lX, dXold, &lXdotdXold));
426:       beta = PetscRealPart(dXdotdX / lXdotdXold);
427:       break;
428:     }
429:     if (ncg->monitor) PetscCall(PetscViewerASCIIPrintf(ncg->monitor, "beta = %e\n", (double)beta));
430:     PetscCall(VecAYPX(lX, beta, dX));
431:   }
432:   PetscCall(PetscInfo(snes, "Maximum number of iterations has been reached: %" PetscInt_FMT "\n", maxits));
433:   if (!snes->reason) snes->reason = SNES_DIVERGED_MAX_IT;
434:   PetscFunctionReturn(PETSC_SUCCESS);
435: }

437: /*MC
438:   SNESNCG - Nonlinear Conjugate-Gradient method for the solution of nonlinear systems.

440:   Level: beginner

442:   Options Database Keys:
443: +   -snes_ncg_type <fr, prp, dy, hs, cd> - Choice of conjugate-gradient update parameter, default is prp.
444: .   -snes_linesearch_type <cp,l2,basic> - Line search type.
445: -   -snes_ncg_monitor - Print the beta values used in the ncg iteration, .

447:    Notes:
448:    This solves the nonlinear system of equations F(x) = 0 using the nonlinear generalization of the conjugate
449:    gradient method.  This may be used with a nonlinear preconditioner used to pick the new search directions, but otherwise
450:    chooses the initial search direction as F(x) for the initial guess x.

452:    Only supports left non-linear preconditioning.

454:    Default line search is `SNESLINESEARCHCP`, unless a nonlinear preconditioner is used with -npc_snes_type <type>, `SNESSetNPC()`, or `SNESGetNPC()` then
455:    `SNESLINESEARCHL2` is used. Also supports the special purpose line search `SNESLINESEARCHNCGLINEAR`

457:    References:
458: .  * -  Peter R. Brune, Matthew G. Knepley, Barry F. Smith, and Xuemin Tu,"Composing Scalable Nonlinear Algebraic Solvers",
459:    SIAM Review, 57(4), 2015

461: .seealso: `SNESCreate()`, `SNES`, `SNESSetType()`, `SNESNEWTONLS`, `SNESNEWTONTR`, `SNESNGMRES`, `SNESQN`, `SNESLINESEARCHNCGLINEAR`, `SNESNCGSetType()`, `SNESLineSearchSetType()`
462: M*/
463: PETSC_EXTERN PetscErrorCode SNESCreate_NCG(SNES snes)
464: {
465:   SNES_NCG *neP;

467:   PetscFunctionBegin;
468:   snes->ops->destroy        = SNESDestroy_NCG;
469:   snes->ops->setup          = SNESSetUp_NCG;
470:   snes->ops->setfromoptions = SNESSetFromOptions_NCG;
471:   snes->ops->view           = SNESView_NCG;
472:   snes->ops->solve          = SNESSolve_NCG;
473:   snes->ops->reset          = SNESReset_NCG;

475:   snes->usesksp = PETSC_FALSE;
476:   snes->usesnpc = PETSC_TRUE;
477:   snes->npcside = PC_LEFT;

479:   snes->alwayscomputesfinalresidual = PETSC_TRUE;

481:   if (!snes->tolerancesset) {
482:     snes->max_funcs = 30000;
483:     snes->max_its   = 10000;
484:     snes->stol      = 1e-20;
485:   }

487:   PetscCall(PetscNew(&neP));
488:   snes->data   = (void *)neP;
489:   neP->monitor = NULL;
490:   neP->type    = SNES_NCG_PRP;
491:   PetscCall(PetscObjectComposeFunction((PetscObject)snes, "SNESNCGSetType_C", SNESNCGSetType_NCG));
492:   PetscFunctionReturn(PETSC_SUCCESS);
493: }