1 #include <../src/snes/impls/richardson/snesrichardsonimpl.h>
2
SNESDestroy_NRichardson(SNES snes)3 static PetscErrorCode SNESDestroy_NRichardson(SNES snes)
4 {
5 PetscFunctionBegin;
6 PetscCall(PetscFree(snes->data));
7 PetscFunctionReturn(PETSC_SUCCESS);
8 }
9
SNESSetUp_NRichardson(SNES snes)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 }
17
SNESSetFromOptions_NRichardson(SNES snes,PetscOptionItems PetscOptionsObject)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 }
25
SNESSolve_NRichardson(SNES snes)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;
32
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);
35
36 snes->reason = SNES_CONVERGED_ITERATING;
37
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 */
42
43 PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
44 snes->iter = 0;
45 snes->norm = 0.;
46 PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
47
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;
59
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 }
73
74 PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
75 snes->norm = fnorm;
76 PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
77 PetscCall(SNESLogConvergenceHistory(snes, fnorm, 0));
78
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);
83
84 /* Call general purpose update function */
85 PetscTryTypeMethod(snes, update, snes->iter);
86
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 }
96
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;
109
110 /* Call general purpose update function */
111 PetscTryTypeMethod(snes, update, snes->iter);
112
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 }
136
137 /*MC
138 SNESNRICHARDSON - Richardson nonlinear solver that uses successive substitutions, also sometimes known as Picard iteration.
139
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.
143
144 Level: beginner
145
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.
152
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`
155
156 This uses no derivative information provided with `SNESSetJacobian()` thus it will be much slower than Newton's method obtained with `-snes_type ls`
157
158 Only supports left non-linear preconditioning.
159
160 .seealso: [](ch_snes), `SNESCreate()`, `SNES`, `SNESSetType()`, `SNESNEWTONLS`, `SNESNEWTONTR`, `SNESNGMRES`, `SNESQN`, `SNESNCG`,
161 `SNESLineSearchSetDamping()`
162 M*/
SNESCreate_NRichardson(SNES snes)163 PETSC_EXTERN PetscErrorCode SNESCreate_NRichardson(SNES snes)
164 {
165 SNES_NRichardson *neP;
166 SNESLineSearch linesearch;
167
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;
173
174 snes->usesksp = PETSC_FALSE;
175 snes->usesnpc = PETSC_TRUE;
176
177 snes->npcside = PC_LEFT;
178
179 PetscCall(SNESGetLineSearch(snes, &linesearch));
180 if (!((PetscObject)linesearch)->type_name) PetscCall(SNESLineSearchSetType(linesearch, SNESLINESEARCHSECANT));
181
182 snes->alwayscomputesfinalresidual = PETSC_TRUE;
183
184 PetscCall(SNESParametersInitialize(snes));
185 PetscObjectParameterSetDefault(snes, max_funcs, 30000);
186 PetscObjectParameterSetDefault(snes, max_its, 10000);
187 PetscObjectParameterSetDefault(snes, stol, 1e-20);
188
189 PetscCall(PetscNew(&neP));
190 snes->data = (void *)neP;
191 PetscFunctionReturn(PETSC_SUCCESS);
192 }
193