Actual source code: snesncg.c
petsc-3.12.5 2020-03-29
1: #include <../src/snes/impls/ncg/snesncgimpl.h>
2: const char *const SNESNCGTypes[] = {"FR","PRP","HS","DY","CD","SNESNCGType","SNES_NCG_",0};
4: static PetscErrorCode SNESReset_NCG(SNES snes)
5: {
7: return(0);
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: {
23: PetscFree(snes->data);
24: return(0);
25: }
27: /*
28: SNESSetUp_NCG - Sets up the internal data structures for the later use
29: of the SNESNCG nonlinear solver.
31: Input Parameters:
32: + snes - the SNES context
33: - x - the solution vector
35: Application Interface Routine: SNESSetUp()
36: */
38: static PetscErrorCode SNESSetUp_NCG(SNES snes)
39: {
43: SNESSetWorkVecs(snes,2);
44: if (snes->npcside== PC_RIGHT) SETERRQ(PetscObjectComm((PetscObject)snes),PETSC_ERR_ARG_WRONGSTATE, "SNESNCG only supports left preconditioning");
45: if (snes->functype == SNES_FUNCTION_DEFAULT) snes->functype = SNES_FUNCTION_UNPRECONDITIONED;
46: return(0);
47: }
49: static PetscErrorCode SNESLineSearchApply_NCGLinear(SNESLineSearch linesearch)
50: {
51: PetscScalar alpha, ptAp;
52: Vec X, Y, F, W;
53: SNES snes;
55: PetscReal *fnorm, *xnorm, *ynorm;
58: SNESLineSearchGetSNES(linesearch, &snes);
59: X = linesearch->vec_sol;
60: W = linesearch->vec_sol_new;
61: F = linesearch->vec_func;
62: Y = linesearch->vec_update;
63: fnorm = &linesearch->fnorm;
64: xnorm = &linesearch->xnorm;
65: ynorm = &linesearch->ynorm;
67: if (!snes->jacobian) {
68: SNESSetUpMatrices(snes);
69: }
71: /*
73: The exact step size for unpreconditioned linear CG is just:
74: alpha = (r, r) / (p, Ap) = (f, f) / (y, Jy)
75: */
76: SNESComputeJacobian(snes, X, snes->jacobian, snes->jacobian_pre);
77: VecDot(F, F, &alpha);
78: MatMult(snes->jacobian, Y, W);
79: VecDot(Y, W, &ptAp);
80: alpha = alpha / ptAp;
81: VecAXPY(X,-alpha,Y);
82: SNESComputeFunction(snes,X,F);
84: VecNorm(F,NORM_2,fnorm);
85: VecNorm(X,NORM_2,xnorm);
86: VecNorm(Y,NORM_2,ynorm);
87: return(0);
88: }
90: /*MC
91: SNESLINESEARCHNCGLINEAR - Special line search only for SNESNCG
93: 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.
94: 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.
96: Notes: This requires a Jacobian-vector product but does not require the solution of a linear system with the Jacobian
98: This is a "odd-ball" line search, we don't know if it is in the literature or used in practice by anyone.
100: Level: advanced
102: .seealso: SNESLineSearchCreate(), SNESLineSearchSetType()
103: M*/
105: PETSC_EXTERN PetscErrorCode SNESLineSearchCreate_NCGLinear(SNESLineSearch linesearch)
106: {
108: linesearch->ops->apply = SNESLineSearchApply_NCGLinear;
109: linesearch->ops->destroy = NULL;
110: linesearch->ops->setfromoptions = NULL;
111: linesearch->ops->reset = NULL;
112: linesearch->ops->view = NULL;
113: linesearch->ops->setup = NULL;
114: return(0);
115: }
117: /*
118: SNESSetFromOptions_NCG - Sets various parameters for the SNESNCG method.
120: Input Parameter:
121: . snes - the SNES context
123: Application Interface Routine: SNESSetFromOptions()
124: */
125: static PetscErrorCode SNESSetFromOptions_NCG(PetscOptionItems *PetscOptionsObject,SNES snes)
126: {
127: SNES_NCG *ncg = (SNES_NCG*)snes->data;
129: PetscBool debug = PETSC_FALSE;
130: SNESNCGType ncgtype=ncg->type;
131: SNESLineSearch linesearch;
134: PetscOptionsHead(PetscOptionsObject,"SNES NCG options");
135: PetscOptionsBool("-snes_ncg_monitor","Monitor the beta values used in the NCG iterations","SNES",ncg->monitor ? PETSC_TRUE : PETSC_FALSE, &debug, NULL);
136: if (debug) {
137: ncg->monitor = PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes));
138: }
139: PetscOptionsEnum("-snes_ncg_type","NCG Beta type used","SNESNCGSetType",SNESNCGTypes,(PetscEnum)ncg->type,(PetscEnum*)&ncgtype,NULL);
140: SNESNCGSetType(snes, ncgtype);
141: PetscOptionsTail();
142: if (!snes->linesearch) {
143: SNESGetLineSearch(snes, &linesearch);
144: if (!snes->npc) {
145: SNESLineSearchSetType(linesearch, SNESLINESEARCHCP);
146: } else {
147: SNESLineSearchSetType(linesearch, SNESLINESEARCHL2);
148: }
149: }
150: return(0);
151: }
153: /*
154: SNESView_NCG - Prints info from the SNESNCG data structure.
156: Input Parameters:
157: + SNES - the SNES context
158: - viewer - visualization context
160: Application Interface Routine: SNESView()
161: */
162: static PetscErrorCode SNESView_NCG(SNES snes, PetscViewer viewer)
163: {
164: SNES_NCG *ncg = (SNES_NCG *) snes->data;
165: PetscBool iascii;
169: PetscObjectTypeCompare((PetscObject) viewer, PETSCVIEWERASCII, &iascii);
170: if (iascii) {
171: PetscViewerASCIIPrintf(viewer, " type: %s\n", SNESNCGTypes[ncg->type]);
172: }
173: return(0);
174: }
176: /*
178: Assuming F = SNESComputeFunction(X) compute Y^tJ^tF using a simple secant approximation of the jacobian.
180: This routine is not currently used. I don't know what its intended purpose is.
182: Note it has a hardwired differencing parameter of 1e-5
184: */
185: PetscErrorCode SNESNCGComputeYtJtF_Private(SNES snes, Vec X, Vec F, Vec Y, Vec W, Vec G, PetscScalar * ytJtf)
186: {
188: PetscScalar ftf, ftg, fty, h;
191: VecDot(F, F, &ftf);
192: VecDot(F, Y, &fty);
193: h = 1e-5*fty / fty;
194: VecCopy(X, W);
195: VecAXPY(W, -h, Y); /* this is arbitrary */
196: SNESComputeFunction(snes, W, G);
197: VecDot(G, F, &ftg);
198: *ytJtf = (ftg - ftf) / h;
199: return(0);
200: }
202: /*@
203: SNESNCGSetType - Sets the conjugate update type for SNESNCG.
205: Logically Collective on SNES
207: Input Parameters:
208: + snes - the iterative context
209: - btype - update type
211: Options Database:
212: . -snes_ncg_type <prp,fr,hs,dy,cd> -strategy for selecting algorithm for computing beta
214: Level: intermediate
216: SNESNCGSelectTypes:
217: + SNES_NCG_FR - Fletcher-Reeves update
218: . SNES_NCG_PRP - Polak-Ribiere-Polyak update
219: . SNES_NCG_HS - Hestenes-Steifel update
220: . SNES_NCG_DY - Dai-Yuan update
221: - SNES_NCG_CD - Conjugate Descent update
223: Notes:
224: SNES_NCG_PRP is the default, and the only one that tolerates generalized search directions.
226: It is not clear what "generalized search directions" means, does it mean use with a nonlinear preconditioner,
227: that is using -npc_snes_type <type>, SNESSetNPC(), or SNESGetNPC()?
229: @*/
230: PetscErrorCode SNESNCGSetType(SNES snes, SNESNCGType btype)
231: {
236: PetscTryMethod(snes,"SNESNCGSetType_C",(SNES,SNESNCGType),(snes,btype));
237: return(0);
238: }
240: static PetscErrorCode SNESNCGSetType_NCG(SNES snes, SNESNCGType btype)
241: {
242: SNES_NCG *ncg = (SNES_NCG*)snes->data;
245: ncg->type = btype;
246: return(0);
247: }
249: /*
250: SNESSolve_NCG - Solves a nonlinear system with the Nonlinear Conjugate Gradient method.
252: Input Parameters:
253: . snes - the SNES context
255: Output Parameter:
256: . outits - number of iterations until termination
258: Application Interface Routine: SNESSolve()
259: */
260: static PetscErrorCode SNESSolve_NCG(SNES snes)
261: {
262: SNES_NCG *ncg = (SNES_NCG*)snes->data;
263: Vec X,dX,lX,F,dXold;
264: PetscReal fnorm, ynorm, xnorm, beta = 0.0;
265: PetscScalar dXdotdX, dXolddotdXold, dXdotdXold, lXdotdX, lXdotdXold;
266: PetscInt maxits, i;
267: PetscErrorCode ierr;
268: SNESLineSearchReason lsresult = SNES_LINESEARCH_SUCCEEDED;
269: SNESLineSearch linesearch;
270: SNESConvergedReason reason;
273: if (snes->xl || snes->xu || snes->ops->computevariablebounds) SETERRQ1(PetscObjectComm((PetscObject)snes),PETSC_ERR_ARG_WRONGSTATE, "SNES solver %s does not support bounds", ((PetscObject)snes)->type_name);
275: PetscCitationsRegister(SNESCitation,&SNEScite);
276: snes->reason = SNES_CONVERGED_ITERATING;
278: maxits = snes->max_its; /* maximum number of iterations */
279: X = snes->vec_sol; /* X^n */
280: dXold = snes->work[0]; /* The previous iterate of X */
281: dX = snes->work[1]; /* the preconditioned direction */
282: lX = snes->vec_sol_update; /* the conjugate direction */
283: F = snes->vec_func; /* residual vector */
285: SNESGetLineSearch(snes, &linesearch);
287: PetscObjectSAWsTakeAccess((PetscObject)snes);
288: snes->iter = 0;
289: snes->norm = 0.;
290: PetscObjectSAWsGrantAccess((PetscObject)snes);
292: /* compute the initial function and preconditioned update dX */
294: if (snes->npc && snes->functype == SNES_FUNCTION_PRECONDITIONED) {
295: SNESApplyNPC(snes,X,NULL,dX);
296: SNESGetConvergedReason(snes->npc,&reason);
297: if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
298: snes->reason = SNES_DIVERGED_INNER;
299: return(0);
300: }
301: VecCopy(dX,F);
302: VecNorm(F,NORM_2,&fnorm);
303: } else {
304: if (!snes->vec_func_init_set) {
305: SNESComputeFunction(snes,X,F);
306: } else snes->vec_func_init_set = PETSC_FALSE;
308: /* convergence test */
309: VecNorm(F,NORM_2,&fnorm);
310: SNESCheckFunctionNorm(snes,fnorm);
311: VecCopy(F,dX);
312: }
313: if (snes->npc) {
314: if (snes->functype == SNES_FUNCTION_UNPRECONDITIONED) {
315: SNESApplyNPC(snes,X,F,dX);
316: SNESGetConvergedReason(snes->npc,&reason);
317: if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
318: snes->reason = SNES_DIVERGED_INNER;
319: return(0);
320: }
321: }
322: }
323: VecCopy(dX,lX);
324: VecDot(dX, dX, &dXdotdX);
327: PetscObjectSAWsTakeAccess((PetscObject)snes);
328: snes->norm = fnorm;
329: PetscObjectSAWsGrantAccess((PetscObject)snes);
330: SNESLogConvergenceHistory(snes,fnorm,0);
331: SNESMonitor(snes,0,fnorm);
333: /* test convergence */
334: (*snes->ops->converged)(snes,0,0.0,0.0,fnorm,&snes->reason,snes->cnvP);
335: if (snes->reason) return(0);
337: /* Call general purpose update function */
338: if (snes->ops->update) {
339: (*snes->ops->update)(snes, snes->iter);
340: }
342: /* first update -- just use the (preconditioned) residual direction for the initial conjugate direction */
344: for (i = 1; i < maxits + 1; i++) {
345: /* some update types require the old update direction or conjugate direction */
346: if (ncg->type != SNES_NCG_FR) {
347: VecCopy(dX, dXold);
348: }
349: SNESLineSearchApply(linesearch,X,F,&fnorm,lX);
350: SNESLineSearchGetReason(linesearch, &lsresult);
351: SNESLineSearchGetNorms(linesearch, &xnorm, &fnorm, &ynorm);
352: if (lsresult) {
353: if (++snes->numFailures >= snes->maxFailures) {
354: snes->reason = SNES_DIVERGED_LINE_SEARCH;
355: return(0);
356: }
357: }
358: if (snes->nfuncs >= snes->max_funcs && snes->max_funcs >= 0) {
359: snes->reason = SNES_DIVERGED_FUNCTION_COUNT;
360: return(0);
361: }
362: /* Monitor convergence */
363: PetscObjectSAWsTakeAccess((PetscObject)snes);
364: snes->iter = i;
365: snes->norm = fnorm;
366: snes->xnorm = xnorm;
367: snes->ynorm = ynorm;
368: PetscObjectSAWsGrantAccess((PetscObject)snes);
369: SNESLogConvergenceHistory(snes,snes->norm,0);
370: SNESMonitor(snes,snes->iter,snes->norm);
372: /* Test for convergence */
373: (*snes->ops->converged)(snes,snes->iter,xnorm,ynorm,fnorm,&snes->reason,snes->cnvP);
374: if (snes->reason) return(0);
376: /* Call general purpose update function */
377: if (snes->ops->update) {
378: (*snes->ops->update)(snes, snes->iter);
379: }
380: if (snes->npc) {
381: if (snes->functype == SNES_FUNCTION_PRECONDITIONED) {
382: SNESApplyNPC(snes,X,NULL,dX);
383: SNESGetConvergedReason(snes->npc,&reason);
384: if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
385: snes->reason = SNES_DIVERGED_INNER;
386: return(0);
387: }
388: VecCopy(dX,F);
389: } else {
390: SNESApplyNPC(snes,X,F,dX);
391: SNESGetConvergedReason(snes->npc,&reason);
392: if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
393: snes->reason = SNES_DIVERGED_INNER;
394: return(0);
395: }
396: }
397: } else {
398: VecCopy(F,dX);
399: }
401: /* compute the conjugate direction lX = dX + beta*lX with beta = ((dX, dX) / (dX_old, dX_old) (Fletcher-Reeves update)*/
402: switch (ncg->type) {
403: case SNES_NCG_FR: /* Fletcher-Reeves */
404: dXolddotdXold= dXdotdX;
405: VecDot(dX, dX, &dXdotdX);
406: beta = PetscRealPart(dXdotdX / dXolddotdXold);
407: break;
408: case SNES_NCG_PRP: /* Polak-Ribiere-Poylak */
409: dXolddotdXold= dXdotdX;
410: VecDotBegin(dX, dX, &dXdotdXold);
411: VecDotBegin(dXold, dX, &dXdotdXold);
412: VecDotEnd(dX, dX, &dXdotdX);
413: VecDotEnd(dXold, dX, &dXdotdXold);
414: beta = PetscRealPart(((dXdotdX - dXdotdXold) / dXolddotdXold));
415: if (beta < 0.0) beta = 0.0; /* restart */
416: break;
417: case SNES_NCG_HS: /* Hestenes-Stiefel */
418: VecDotBegin(dX, dX, &dXdotdX);
419: VecDotBegin(dX, dXold, &dXdotdXold);
420: VecDotBegin(lX, dX, &lXdotdX);
421: VecDotBegin(lX, dXold, &lXdotdXold);
422: VecDotEnd(dX, dX, &dXdotdX);
423: VecDotEnd(dX, dXold, &dXdotdXold);
424: VecDotEnd(lX, dX, &lXdotdX);
425: VecDotEnd(lX, dXold, &lXdotdXold);
426: beta = PetscRealPart((dXdotdX - dXdotdXold) / (lXdotdX - lXdotdXold));
427: break;
428: case SNES_NCG_DY: /* Dai-Yuan */
429: VecDotBegin(dX, dX, &dXdotdX);
430: VecDotBegin(lX, dX, &lXdotdX);
431: VecDotBegin(lX, dXold, &lXdotdXold);
432: VecDotEnd(dX, dX, &dXdotdX);
433: VecDotEnd(lX, dX, &lXdotdX);
434: VecDotEnd(lX, dXold, &lXdotdXold);
435: beta = PetscRealPart(dXdotdX / (lXdotdXold - lXdotdX));
436: break;
437: case SNES_NCG_CD: /* Conjugate Descent */
438: VecDotBegin(dX, dX, &dXdotdX);
439: VecDotBegin(lX, dXold, &lXdotdXold);
440: VecDotEnd(dX, dX, &dXdotdX);
441: VecDotEnd(lX, dXold, &lXdotdXold);
442: beta = PetscRealPart(dXdotdX / lXdotdXold);
443: break;
444: }
445: if (ncg->monitor) {
446: PetscViewerASCIIPrintf(ncg->monitor, "beta = %e\n", (double)beta);
447: }
448: VecAYPX(lX, beta, dX);
449: }
450: PetscInfo1(snes, "Maximum number of iterations has been reached: %D\n", maxits);
451: if (!snes->reason) snes->reason = SNES_DIVERGED_MAX_IT;
452: return(0);
453: }
455: /*MC
456: SNESNCG - Nonlinear Conjugate-Gradient method for the solution of general nonlinear systems.
458: Level: beginner
460: Options Database:
461: + -snes_ncg_type <fr, prp, dy, hs, cd> - Choice of conjugate-gradient update parameter, default is prp.
462: . -snes_linesearch_type <cp,l2,basic> - Line search type.
463: - -snes_ncg_monitor - Print the beta values used in the ncg iteration, .
465: Notes:
466: This solves the nonlinear system of equations F(x) = 0 using the nonlinear generalization of the conjugate
467: gradient method. This may be used with a nonlinear preconditioner used to pick the new search directions, but otherwise
468: chooses the initial search direction as F(x) for the initial guess x.
470: Only supports left non-linear preconditioning.
472: Default line search is SNESLINESEARCHCP, unless a nonlinear preconditioner is used with -npc_snes_type <type>, SNESSetNPC(), or SNESGetNPC() then
473: SNESLINESEARCHL2 is used. Also supports the special purpose line search SNESLINESEARCHNCGLINEAR
475: References:
476: . 1. - Peter R. Brune, Matthew G. Knepley, Barry F. Smith, and Xuemin Tu,"Composing Scalable Nonlinear Algebraic Solvers",
477: SIAM Review, 57(4), 2015
480: .seealso: SNESCreate(), SNES, SNESSetType(), SNESNEWTONLS, SNESNEWTONTR, SNESNGMRES, SNESQN, SNESLINESEARCHNCGLINEAR, SNESNCGSetType(), SNESNCGGetType(), SNESLineSearchSetType()
481: M*/
482: PETSC_EXTERN PetscErrorCode SNESCreate_NCG(SNES snes)
483: {
485: SNES_NCG * neP;
488: snes->ops->destroy = SNESDestroy_NCG;
489: snes->ops->setup = SNESSetUp_NCG;
490: snes->ops->setfromoptions = SNESSetFromOptions_NCG;
491: snes->ops->view = SNESView_NCG;
492: snes->ops->solve = SNESSolve_NCG;
493: snes->ops->reset = SNESReset_NCG;
495: snes->usesksp = PETSC_FALSE;
496: snes->usesnpc = PETSC_TRUE;
497: snes->npcside = PC_LEFT;
499: snes->alwayscomputesfinalresidual = PETSC_TRUE;
501: if (!snes->tolerancesset) {
502: snes->max_funcs = 30000;
503: snes->max_its = 10000;
504: snes->stol = 1e-20;
505: }
507: PetscNewLog(snes,&neP);
508: snes->data = (void*) neP;
509: neP->monitor = NULL;
510: neP->type = SNES_NCG_PRP;
511: PetscObjectComposeFunction((PetscObject)snes,"SNESNCGSetType_C", SNESNCGSetType_NCG);
512: return(0);
513: }