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