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 SNESSolve_NRichardson(SNES snes)
27: {
28: Vec X, Y, F;
29: PetscReal xnorm, fnorm, ynorm;
30: PetscInt maxits, i;
31: SNESLineSearchReason lsresult;
32: SNESConvergedReason reason;
34: PetscFunctionBegin;
35: 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);
37: snes->reason = SNES_CONVERGED_ITERATING;
39: maxits = snes->max_its; /* maximum number of iterations */
40: X = snes->vec_sol; /* X^n */
41: Y = snes->vec_sol_update; /* \tilde X */
42: F = snes->vec_func; /* residual vector */
44: PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
45: snes->iter = 0;
46: snes->norm = 0.;
47: PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
49: if (snes->npc && snes->functype == SNES_FUNCTION_PRECONDITIONED) {
50: PetscCall(SNESApplyNPC(snes, X, NULL, F));
51: PetscCall(SNESGetConvergedReason(snes->npc, &reason));
52: if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
53: snes->reason = SNES_DIVERGED_INNER;
54: PetscFunctionReturn(PETSC_SUCCESS);
55: }
56: PetscCall(VecNorm(F, NORM_2, &fnorm));
57: } else {
58: if (!snes->vec_func_init_set) PetscCall(SNESComputeFunction(snes, X, F));
59: else snes->vec_func_init_set = PETSC_FALSE;
61: PetscCall(VecNorm(F, NORM_2, &fnorm));
62: SNESCheckFunctionNorm(snes, fnorm);
63: }
64: if (snes->npc && snes->functype == SNES_FUNCTION_UNPRECONDITIONED) {
65: PetscCall(SNESApplyNPC(snes, X, F, Y));
66: PetscCall(SNESGetConvergedReason(snes->npc, &reason));
67: if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
68: snes->reason = SNES_DIVERGED_INNER;
69: PetscFunctionReturn(PETSC_SUCCESS);
70: }
71: } else {
72: PetscCall(VecCopy(F, Y));
73: }
75: PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
76: snes->norm = fnorm;
77: PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
78: PetscCall(SNESLogConvergenceHistory(snes, fnorm, 0));
80: /* test convergence */
81: PetscCall(SNESConverged(snes, 0, 0.0, 0.0, fnorm));
82: PetscCall(SNESMonitor(snes, 0, fnorm));
83: if (snes->reason) PetscFunctionReturn(PETSC_SUCCESS);
85: /* Call general purpose update function */
86: PetscTryTypeMethod(snes, update, snes->iter);
88: for (i = 1; i < maxits + 1; i++) {
89: PetscCall(SNESLineSearchApply(snes->linesearch, X, F, &fnorm, Y));
90: PetscCall(SNESLineSearchGetReason(snes->linesearch, &lsresult));
91: PetscCall(SNESLineSearchGetNorms(snes->linesearch, &xnorm, &fnorm, &ynorm));
92: if (lsresult) {
93: if (++snes->numFailures >= snes->maxFailures) {
94: snes->reason = SNES_DIVERGED_LINE_SEARCH;
95: break;
96: }
97: }
98: if (snes->nfuncs >= snes->max_funcs && snes->max_funcs >= 0) {
99: snes->reason = SNES_DIVERGED_FUNCTION_COUNT;
100: break;
101: }
103: /* Monitor convergence */
104: PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
105: snes->iter = i;
106: snes->norm = fnorm;
107: snes->xnorm = xnorm;
108: snes->ynorm = ynorm;
109: PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
110: PetscCall(SNESLogConvergenceHistory(snes, snes->norm, 0));
111: /* Test for convergence */
112: PetscCall(SNESConverged(snes, snes->iter, xnorm, ynorm, fnorm));
113: PetscCall(SNESMonitor(snes, snes->iter, snes->norm));
114: if (snes->reason) break;
116: /* Call general purpose update function */
117: PetscTryTypeMethod(snes, update, snes->iter);
119: if (snes->npc) {
120: if (snes->functype == SNES_FUNCTION_PRECONDITIONED) {
121: PetscCall(SNESApplyNPC(snes, X, NULL, Y));
122: PetscCall(VecNorm(F, NORM_2, &fnorm));
123: PetscCall(VecCopy(Y, F));
124: } else {
125: PetscCall(SNESApplyNPC(snes, X, F, Y));
126: }
127: PetscCall(SNESGetConvergedReason(snes->npc, &reason));
128: if (reason < 0 && reason != SNES_DIVERGED_MAX_IT) {
129: snes->reason = SNES_DIVERGED_INNER;
130: PetscFunctionReturn(PETSC_SUCCESS);
131: }
132: } else {
133: PetscCall(VecCopy(F, Y));
134: }
135: }
136: if (i == maxits + 1) {
137: PetscCall(PetscInfo(snes, "Maximum number of iterations has been reached: %" PetscInt_FMT "\n", maxits));
138: if (!snes->reason) snes->reason = SNES_DIVERGED_MAX_IT;
139: }
140: PetscFunctionReturn(PETSC_SUCCESS);
141: }
143: /*MC
144: SNESNRICHARDSON - Richardson nonlinear solver that uses successive substitutions, also sometimes known as Picard iteration.
146: Options Database Keys:
147: + -snes_linesearch_type <l2,cp,basic> - Line search type.
148: - -snes_linesearch_damping <1.0> - Damping for the line search.
150: Level: beginner
152: Notes:
153: If no inner nonlinear preconditioner is provided then solves $F(x) - b = 0 $ using $x^{n+1} = x^{n} - \lambda
154: (F(x^n) - b) $ where $ \lambda$ is obtained with either `SNESLineSearchSetDamping()`, `-snes_damping` or a line search. If
155: an inner nonlinear preconditioner is provided (either with `-npc_snes_typ`e or `SNESSetNPC()`) then the inner
156: solver is called on the initial solution $x^n$ and the nonlinear Richardson uses $ x^{n+1} = x^{n} + \lambda d^{n}$
157: where $d^{n} = \hat{x}^{n} - x^{n} $ where $\hat{x}^{n} $ is the solution returned from the inner solver.
159: The update, especially without inner nonlinear preconditioner, may be ill-scaled. If using the basic
160: linesearch, one may have to scale the update with `-snes_linesearch_damping`
162: This uses no derivative information provided with `SNESSetJacobian()` thus it will be much slower than Newton's method obtained with `-snes_type ls`
164: Only supports left non-linear preconditioning.
166: .seealso: [](ch_snes), `SNESCreate()`, `SNES`, `SNESSetType()`, `SNESNEWTONLS`, `SNESNEWTONTR`, `SNESNGMRES`, `SNESQN`, `SNESNCG`,
167: `SNESLineSearchSetDamping()`
168: M*/
169: PETSC_EXTERN PetscErrorCode SNESCreate_NRichardson(SNES snes)
170: {
171: SNES_NRichardson *neP;
172: SNESLineSearch linesearch;
174: PetscFunctionBegin;
175: snes->ops->destroy = SNESDestroy_NRichardson;
176: snes->ops->setup = SNESSetUp_NRichardson;
177: snes->ops->setfromoptions = SNESSetFromOptions_NRichardson;
178: snes->ops->solve = SNESSolve_NRichardson;
180: snes->usesksp = PETSC_FALSE;
181: snes->usesnpc = PETSC_TRUE;
183: snes->npcside = PC_LEFT;
185: PetscCall(SNESGetLineSearch(snes, &linesearch));
186: if (!((PetscObject)linesearch)->type_name) PetscCall(SNESLineSearchSetType(linesearch, SNESLINESEARCHSECANT));
188: snes->alwayscomputesfinalresidual = PETSC_TRUE;
190: PetscCall(SNESParametersInitialize(snes));
191: PetscObjectParameterSetDefault(snes, max_funcs, 30000);
192: PetscObjectParameterSetDefault(snes, max_its, 10000);
193: PetscObjectParameterSetDefault(snes, stol, 1e-20);
195: PetscCall(PetscNew(&neP));
196: snes->data = (void *)neP;
197: PetscFunctionReturn(PETSC_SUCCESS);
198: }