Actual source code: snesrichardson.c
1: #include <../src/snes/impls/richardson/snesrichardsonimpl.h>
3: static PetscErrorCode SNESDestroy_NRichardson(SNES snes)
4: {
5: PetscFunctionBegin;
6: PetscCall(PetscFree(snes->data));
7: PetscFunctionReturn(PETSC_SUCCESS);
8: }
10: static PetscErrorCode SNESSetUp_NRichardson(SNES snes)
11: {
12: PetscFunctionBegin;
13: PetscCheck(snes->npcside != PC_RIGHT, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "NRichardson only supports left preconditioning");
14: if (snes->functype == SNES_FUNCTION_DEFAULT) snes->functype = SNES_FUNCTION_UNPRECONDITIONED;
15: PetscFunctionReturn(PETSC_SUCCESS);
16: }
18: static PetscErrorCode SNESSetFromOptions_NRichardson(SNES snes, PetscOptionItems PetscOptionsObject)
19: {
20: PetscFunctionBegin;
21: PetscOptionsHeadBegin(PetscOptionsObject, "SNES Richardson options");
22: PetscOptionsHeadEnd();
23: PetscFunctionReturn(PETSC_SUCCESS);
24: }
26: static PetscErrorCode SNESView_NRichardson(SNES snes, PetscViewer viewer)
27: {
28: PetscBool isascii;
30: PetscFunctionBegin;
31: PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isascii));
32: if (isascii) { }
33: PetscFunctionReturn(PETSC_SUCCESS);
34: }
36: static PetscErrorCode SNESSolve_NRichardson(SNES snes)
37: {
38: Vec X, Y, F;
39: PetscReal xnorm, fnorm, ynorm;
40: PetscInt maxits, i;
41: SNESLineSearchReason lsresult;
42: SNESConvergedReason reason;
44: PetscFunctionBegin;
45: 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);
47: snes->reason = SNES_CONVERGED_ITERATING;
49: maxits = snes->max_its; /* maximum number of iterations */
50: X = snes->vec_sol; /* X^n */
51: Y = snes->vec_sol_update; /* \tilde X */
52: F = snes->vec_func; /* residual vector */
54: PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
55: snes->iter = 0;
56: snes->norm = 0.;
57: PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
59: if (snes->npc && snes->functype == SNES_FUNCTION_PRECONDITIONED) {
60: PetscCall(SNESApplyNPC(snes, X, NULL, F));
61: PetscCall(SNESGetConvergedReason(snes->npc, &reason));
62: if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
63: snes->reason = SNES_DIVERGED_INNER;
64: PetscFunctionReturn(PETSC_SUCCESS);
65: }
66: PetscCall(VecNorm(F, NORM_2, &fnorm));
67: } else {
68: if (!snes->vec_func_init_set) PetscCall(SNESComputeFunction(snes, X, F));
69: else snes->vec_func_init_set = PETSC_FALSE;
71: PetscCall(VecNorm(F, NORM_2, &fnorm));
72: SNESCheckFunctionNorm(snes, fnorm);
73: }
74: if (snes->npc && snes->functype == SNES_FUNCTION_UNPRECONDITIONED) {
75: PetscCall(SNESApplyNPC(snes, X, F, Y));
76: PetscCall(SNESGetConvergedReason(snes->npc, &reason));
77: if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
78: snes->reason = SNES_DIVERGED_INNER;
79: PetscFunctionReturn(PETSC_SUCCESS);
80: }
81: } else {
82: PetscCall(VecCopy(F, Y));
83: }
85: PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
86: snes->norm = fnorm;
87: PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
88: PetscCall(SNESLogConvergenceHistory(snes, fnorm, 0));
90: /* test convergence */
91: PetscCall(SNESConverged(snes, 0, 0.0, 0.0, fnorm));
92: PetscCall(SNESMonitor(snes, 0, fnorm));
93: if (snes->reason) PetscFunctionReturn(PETSC_SUCCESS);
95: /* Call general purpose update function */
96: PetscTryTypeMethod(snes, update, snes->iter);
98: for (i = 1; i < maxits + 1; i++) {
99: PetscCall(SNESLineSearchApply(snes->linesearch, X, F, &fnorm, Y));
100: PetscCall(SNESLineSearchGetReason(snes->linesearch, &lsresult));
101: PetscCall(SNESLineSearchGetNorms(snes->linesearch, &xnorm, &fnorm, &ynorm));
102: if (lsresult) {
103: if (++snes->numFailures >= snes->maxFailures) {
104: snes->reason = SNES_DIVERGED_LINE_SEARCH;
105: break;
106: }
107: }
108: if (snes->nfuncs >= snes->max_funcs && snes->max_funcs >= 0) {
109: snes->reason = SNES_DIVERGED_FUNCTION_COUNT;
110: break;
111: }
113: /* Monitor convergence */
114: PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
115: snes->iter = i;
116: snes->norm = fnorm;
117: snes->xnorm = xnorm;
118: snes->ynorm = ynorm;
119: PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
120: PetscCall(SNESLogConvergenceHistory(snes, snes->norm, 0));
121: /* Test for convergence */
122: PetscCall(SNESConverged(snes, snes->iter, xnorm, ynorm, fnorm));
123: PetscCall(SNESMonitor(snes, snes->iter, snes->norm));
124: if (snes->reason) break;
126: /* Call general purpose update function */
127: PetscTryTypeMethod(snes, update, snes->iter);
129: if (snes->npc) {
130: if (snes->functype == SNES_FUNCTION_PRECONDITIONED) {
131: PetscCall(SNESApplyNPC(snes, X, NULL, Y));
132: PetscCall(VecNorm(F, NORM_2, &fnorm));
133: PetscCall(VecCopy(Y, F));
134: } else {
135: PetscCall(SNESApplyNPC(snes, X, F, Y));
136: }
137: PetscCall(SNESGetConvergedReason(snes->npc, &reason));
138: if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
139: snes->reason = SNES_DIVERGED_INNER;
140: PetscFunctionReturn(PETSC_SUCCESS);
141: }
142: } else {
143: PetscCall(VecCopy(F, Y));
144: }
145: }
146: if (i == maxits + 1) {
147: PetscCall(PetscInfo(snes, "Maximum number of iterations has been reached: %" PetscInt_FMT "\n", maxits));
148: if (!snes->reason) snes->reason = SNES_DIVERGED_MAX_IT;
149: }
150: PetscFunctionReturn(PETSC_SUCCESS);
151: }
153: /*MC
154: SNESNRICHARDSON - Richardson nonlinear solver that uses successive substitutions, also sometimes known as Picard iteration.
156: Options Database Keys:
157: + -snes_linesearch_type <l2,cp,basic> - Line search type.
158: - -snes_linesearch_damping <1.0> - Damping for the line search.
160: Level: beginner
162: Notes:
163: If no inner nonlinear preconditioner is provided then solves $F(x) - b = 0 $ using $x^{n+1} = x^{n} - \lambda
164: (F(x^n) - b) $ where $ \lambda$ is obtained with either `SNESLineSearchSetDamping()`, `-snes_damping` or a line search. If
165: an inner nonlinear preconditioner is provided (either with `-npc_snes_typ`e or `SNESSetNPC()`) then the inner
166: solver is called on the initial solution $x^n$ and the nonlinear Richardson uses $ x^{n+1} = x^{n} + \lambda d^{n}$
167: where $d^{n} = \hat{x}^{n} - x^{n} $ where $\hat{x}^{n} $ is the solution returned from the inner solver.
169: The update, especially without inner nonlinear preconditioner, may be ill-scaled. If using the basic
170: linesearch, one may have to scale the update with `-snes_linesearch_damping`
172: This uses no derivative information provided with `SNESSetJacobian()` thus it will be much slower than Newton's method obtained with `-snes_type ls`
174: Only supports left non-linear preconditioning.
176: .seealso: [](ch_snes), `SNESCreate()`, `SNES`, `SNESSetType()`, `SNESNEWTONLS`, `SNESNEWTONTR`, `SNESNGMRES`, `SNESQN`, `SNESNCG`,
177: `SNESLineSearchSetDamping()`
178: M*/
179: PETSC_EXTERN PetscErrorCode SNESCreate_NRichardson(SNES snes)
180: {
181: SNES_NRichardson *neP;
182: SNESLineSearch linesearch;
184: PetscFunctionBegin;
185: snes->ops->destroy = SNESDestroy_NRichardson;
186: snes->ops->setup = SNESSetUp_NRichardson;
187: snes->ops->setfromoptions = SNESSetFromOptions_NRichardson;
188: snes->ops->view = SNESView_NRichardson;
189: snes->ops->solve = SNESSolve_NRichardson;
191: snes->usesksp = PETSC_FALSE;
192: snes->usesnpc = PETSC_TRUE;
194: snes->npcside = PC_LEFT;
196: PetscCall(SNESGetLineSearch(snes, &linesearch));
197: if (!((PetscObject)linesearch)->type_name) PetscCall(SNESLineSearchSetType(linesearch, SNESLINESEARCHSECANT));
199: snes->alwayscomputesfinalresidual = PETSC_TRUE;
201: PetscCall(SNESParametersInitialize(snes));
202: PetscObjectParameterSetDefault(snes, max_funcs, 30000);
203: PetscObjectParameterSetDefault(snes, max_its, 10000);
204: PetscObjectParameterSetDefault(snes, stol, 1e-20);
206: PetscCall(PetscNew(&neP));
207: snes->data = (void *)neP;
208: PetscFunctionReturn(PETSC_SUCCESS);
209: }