Actual source code: snesgs.c
1: #include <../src/snes/impls/gs/gsimpl.h>
3: /*@
4: SNESNGSSetTolerances - Sets various parameters used in convergence tests for nonlinear Gauss-Seidel `SNESNCG`
6: Logically Collective
8: Input Parameters:
9: + snes - the `SNES` context
10: . abstol - absolute convergence tolerance
11: . rtol - relative convergence tolerance
12: . stol - convergence tolerance in terms of the norm of the change in the solution between steps, || delta x || < stol*|| x ||
13: - maxit - maximum number of iterations
15: Options Database Keys:
16: + -snes_ngs_atol <abstol> - Sets abstol
17: . -snes_ngs_rtol <rtol> - Sets rtol
18: . -snes_ngs_stol <stol> - Sets stol
19: - -snes_max_it <maxit> - Sets maxit
21: Level: intermediate
23: .seealso: `SNESNCG`, `SNESSetTrustRegionTolerance()`
24: @*/
25: PetscErrorCode SNESNGSSetTolerances(SNES snes, PetscReal abstol, PetscReal rtol, PetscReal stol, PetscInt maxit)
26: {
27: SNES_NGS *gs = (SNES_NGS *)snes->data;
29: PetscFunctionBegin;
32: if (abstol != (PetscReal)PETSC_DEFAULT) {
33: PetscCheck(abstol >= 0.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Absolute tolerance %g must be non-negative", (double)abstol);
34: gs->abstol = abstol;
35: }
36: if (rtol != (PetscReal)PETSC_DEFAULT) {
37: PetscCheck(rtol >= 0.0 && rtol < 1.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Relative tolerance %g must be non-negative and less than 1.0", (double)rtol);
38: gs->rtol = rtol;
39: }
40: if (stol != (PetscReal)PETSC_DEFAULT) {
41: PetscCheck(stol >= 0.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Step tolerance %g must be non-negative", (double)stol);
42: gs->stol = stol;
43: }
44: if (maxit != PETSC_DEFAULT) {
45: PetscCheck(maxit >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Maximum number of iterations %" PetscInt_FMT " must be non-negative", maxit);
46: gs->max_its = maxit;
47: }
48: PetscFunctionReturn(PETSC_SUCCESS);
49: }
51: /*@
52: SNESNGSGetTolerances - Gets various parameters used in convergence tests for nonlinear Gauss-Seidel `SNESNCG`
54: Not Collective
56: Input Parameters:
57: + snes - the `SNES` context
58: . atol - absolute convergence tolerance
59: . rtol - relative convergence tolerance
60: . stol - convergence tolerance in terms of the norm
61: of the change in the solution between steps
62: - maxit - maximum number of iterations
64: Level: intermediate
66: Note:
67: The user can specify NULL for any parameter that is not needed.
69: .seealso: `SNESNCG`, `SNESSetTolerances()`
70: @*/
71: PetscErrorCode SNESNGSGetTolerances(SNES snes, PetscReal *atol, PetscReal *rtol, PetscReal *stol, PetscInt *maxit)
72: {
73: SNES_NGS *gs = (SNES_NGS *)snes->data;
75: PetscFunctionBegin;
77: if (atol) *atol = gs->abstol;
78: if (rtol) *rtol = gs->rtol;
79: if (stol) *stol = gs->stol;
80: if (maxit) *maxit = gs->max_its;
81: PetscFunctionReturn(PETSC_SUCCESS);
82: }
84: /*@
85: SNESNGSSetSweeps - Sets the number of sweeps of nonlinear GS to use in `SNESNCG`
87: Input Parameters:
88: + snes - the `SNES` context
89: - sweeps - the number of sweeps of nonlinear GS to perform.
91: Options Database Key:
92: . -snes_ngs_sweeps <n> - Number of sweeps of nonlinear GS to apply
94: Level: intermediate
96: .seealso: `SNESNCG`, `SNESSetNGS()`, `SNESGetNGS()`, `SNESSetNPC()`, `SNESNGSGetSweeps()`
97: @*/
98: PetscErrorCode SNESNGSSetSweeps(SNES snes, PetscInt sweeps)
99: {
100: SNES_NGS *gs = (SNES_NGS *)snes->data;
102: PetscFunctionBegin;
104: gs->sweeps = sweeps;
105: PetscFunctionReturn(PETSC_SUCCESS);
106: }
108: /*@
109: SNESNGSGetSweeps - Gets the number of sweeps nonlinear GS will use in `SNESNCG`
111: Input Parameter:
112: . snes - the `SNES` context
114: Output Parameter:
115: . sweeps - the number of sweeps of nonlinear GS to perform.
117: Level: intermediate
119: .seealso: `SNESNCG`, `SNESSetNGS()`, `SNESGetNGS()`, `SNESSetNPC()`, `SNESNGSSetSweeps()`
120: @*/
121: PetscErrorCode SNESNGSGetSweeps(SNES snes, PetscInt *sweeps)
122: {
123: SNES_NGS *gs = (SNES_NGS *)snes->data;
125: PetscFunctionBegin;
127: *sweeps = gs->sweeps;
128: PetscFunctionReturn(PETSC_SUCCESS);
129: }
131: static PetscErrorCode SNESReset_NGS(SNES snes)
132: {
133: SNES_NGS *gs = (SNES_NGS *)snes->data;
135: PetscFunctionBegin;
136: PetscCall(ISColoringDestroy(&gs->coloring));
137: PetscFunctionReturn(PETSC_SUCCESS);
138: }
140: static PetscErrorCode SNESDestroy_NGS(SNES snes)
141: {
142: PetscFunctionBegin;
143: PetscCall(SNESReset_NGS(snes));
144: PetscCall(PetscFree(snes->data));
145: PetscFunctionReturn(PETSC_SUCCESS);
146: }
148: static PetscErrorCode SNESSetUp_NGS(SNES snes)
149: {
150: PetscErrorCode (*f)(SNES, Vec, Vec, void *);
152: PetscFunctionBegin;
153: PetscCall(SNESGetNGS(snes, &f, NULL));
154: if (!f) PetscCall(SNESSetNGS(snes, SNESComputeNGSDefaultSecant, NULL));
155: PetscFunctionReturn(PETSC_SUCCESS);
156: }
158: static PetscErrorCode SNESSetFromOptions_NGS(SNES snes, PetscOptionItems *PetscOptionsObject)
159: {
160: SNES_NGS *gs = (SNES_NGS *)snes->data;
161: PetscInt sweeps, max_its = PETSC_DEFAULT;
162: PetscReal rtol = PETSC_DEFAULT, atol = PETSC_DEFAULT, stol = PETSC_DEFAULT;
163: PetscBool flg, flg1, flg2, flg3;
165: PetscFunctionBegin;
166: PetscOptionsHeadBegin(PetscOptionsObject, "SNES GS options");
167: /* GS Options */
168: PetscCall(PetscOptionsInt("-snes_ngs_sweeps", "Number of sweeps of GS to apply", "SNESComputeGS", gs->sweeps, &sweeps, &flg));
169: if (flg) PetscCall(SNESNGSSetSweeps(snes, sweeps));
170: PetscCall(PetscOptionsReal("-snes_ngs_atol", "Absolute residual tolerance for GS iteration", "SNESComputeGS", gs->abstol, &atol, &flg));
171: PetscCall(PetscOptionsReal("-snes_ngs_rtol", "Relative residual tolerance for GS iteration", "SNESComputeGS", gs->rtol, &rtol, &flg1));
172: PetscCall(PetscOptionsReal("-snes_ngs_stol", "Absolute update tolerance for GS iteration", "SNESComputeGS", gs->stol, &stol, &flg2));
173: PetscCall(PetscOptionsInt("-snes_ngs_max_it", "Maximum number of sweeps of GS to apply", "SNESComputeGS", gs->max_its, &max_its, &flg3));
174: if (flg || flg1 || flg2 || flg3) PetscCall(SNESNGSSetTolerances(snes, atol, rtol, stol, max_its));
175: flg = PETSC_FALSE;
176: PetscCall(PetscOptionsBool("-snes_ngs_secant", "Use finite difference secant approximation with coloring", "", flg, &flg, NULL));
177: if (flg) {
178: PetscCall(SNESSetNGS(snes, SNESComputeNGSDefaultSecant, NULL));
179: PetscCall(PetscInfo(snes, "Setting default finite difference secant approximation with coloring\n"));
180: }
181: PetscCall(PetscOptionsReal("-snes_ngs_secant_h", "Differencing parameter for secant search", "", gs->h, &gs->h, NULL));
182: PetscCall(PetscOptionsBool("-snes_ngs_secant_mat_coloring", "Use the graph coloring of the Jacobian for the secant GS", "", gs->secant_mat, &gs->secant_mat, &flg));
184: PetscOptionsHeadEnd();
185: PetscFunctionReturn(PETSC_SUCCESS);
186: }
188: static PetscErrorCode SNESView_NGS(SNES snes, PetscViewer viewer)
189: {
190: PetscErrorCode (*f)(SNES, Vec, Vec, void *);
191: SNES_NGS *gs = (SNES_NGS *)snes->data;
192: PetscBool iascii;
194: PetscFunctionBegin;
195: PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &iascii));
196: if (iascii) {
197: PetscCall(DMSNESGetNGS(snes->dm, &f, NULL));
198: if (f == SNESComputeNGSDefaultSecant) PetscCall(PetscViewerASCIIPrintf(viewer, " Use finite difference secant approximation with coloring with h = %g \n", (double)gs->h));
199: }
200: PetscFunctionReturn(PETSC_SUCCESS);
201: }
203: static PetscErrorCode SNESSolve_NGS(SNES snes)
204: {
205: Vec F;
206: Vec X;
207: Vec B;
208: PetscInt i;
209: PetscReal fnorm;
210: SNESNormSchedule normschedule;
212: PetscFunctionBegin;
214: 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);
216: PetscCall(PetscCitationsRegister(SNESCitation, &SNEScite));
217: X = snes->vec_sol;
218: F = snes->vec_func;
219: B = snes->vec_rhs;
221: PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
222: snes->iter = 0;
223: snes->norm = 0.;
224: PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
225: snes->reason = SNES_CONVERGED_ITERATING;
227: PetscCall(SNESGetNormSchedule(snes, &normschedule));
228: if (normschedule == SNES_NORM_ALWAYS || normschedule == SNES_NORM_INITIAL_ONLY || normschedule == SNES_NORM_INITIAL_FINAL_ONLY) {
229: /* compute the initial function and preconditioned update delX */
230: if (!snes->vec_func_init_set) {
231: PetscCall(SNESComputeFunction(snes, X, F));
232: } else snes->vec_func_init_set = PETSC_FALSE;
234: PetscCall(VecNorm(F, NORM_2, &fnorm)); /* fnorm <- ||F|| */
235: SNESCheckFunctionNorm(snes, fnorm);
236: PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
237: snes->iter = 0;
238: snes->norm = fnorm;
239: PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
240: PetscCall(SNESLogConvergenceHistory(snes, snes->norm, 0));
242: /* test convergence */
243: PetscCall(SNESConverged(snes, 0, 0.0, 0.0, fnorm));
244: PetscCall(SNESMonitor(snes, 0, snes->norm));
245: if (snes->reason) PetscFunctionReturn(PETSC_SUCCESS);
246: } else {
247: PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
248: PetscCall(SNESLogConvergenceHistory(snes, snes->norm, 0));
249: }
251: /* Call general purpose update function */
252: PetscTryTypeMethod(snes, update, snes->iter);
254: for (i = 0; i < snes->max_its; i++) {
255: PetscCall(SNESComputeNGS(snes, B, X));
256: /* only compute norms if requested or about to exit due to maximum iterations */
257: if (normschedule == SNES_NORM_ALWAYS || ((i == snes->max_its - 1) && (normschedule == SNES_NORM_INITIAL_FINAL_ONLY || normschedule == SNES_NORM_FINAL_ONLY))) {
258: PetscCall(SNESComputeFunction(snes, X, F));
259: PetscCall(VecNorm(F, NORM_2, &fnorm)); /* fnorm <- ||F|| */
260: SNESCheckFunctionNorm(snes, fnorm);
261: }
262: /* Monitor convergence */
263: PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
264: snes->iter = i + 1;
265: snes->norm = fnorm;
266: PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
267: PetscCall(SNESLogConvergenceHistory(snes, snes->norm, snes->iter));
268: /* Test for convergence */
269: PetscCall(SNESConverged(snes, snes->iter, 0.0, 0.0, fnorm));
270: PetscCall(SNESMonitor(snes, snes->iter, snes->norm));
271: if (snes->reason) PetscFunctionReturn(PETSC_SUCCESS);
272: /* Call general purpose update function */
273: PetscTryTypeMethod(snes, update, snes->iter);
274: }
275: PetscFunctionReturn(PETSC_SUCCESS);
276: }
278: /*MC
279: SNESNGS - Either calls the user-provided solution routine provided with `SNESSetNGS()` or does a finite difference secant approximation
280: using coloring.
282: Level: advanced
284: Options Database Keys:
285: + -snes_ngs_sweeps <n> - Number of sweeps of nonlinear GS to apply
286: . -snes_ngs_atol <atol> - Absolute residual tolerance for nonlinear GS iteration
287: . -snes_ngs_rtol <rtol> - Relative residual tolerance for nonlinear GS iteration
288: . -snes_ngs_stol <stol> - Absolute update tolerance for nonlinear GS iteration
289: . -snes_ngs_max_it <maxit> - Maximum number of sweeps of nonlinea GS to apply
290: . -snes_ngs_secant - Use pointwise secant local Jacobian approximation with coloring instead of user provided Gauss-Seidel routine, this is
291: used by default if no user provided Gauss-Seidel routine is available. Requires either that a `DM` that can compute a coloring
292: is available or a Jacobian sparse matrix is provided (from which to get the coloring).
293: . -snes_ngs_secant_h <h> - Differencing parameter for secant approximation
294: . -snes_ngs_secant_mat_coloring - Use the graph coloring of the Jacobian for the secant GS even if a DM is available.
295: - -snes_norm_schedule <none, always, initialonly, finalonly, initialfinalonly> - how often the residual norms are computed
297: Notes:
298: the Gauss-Seidel smoother is inherited through composition. If a solver has been created with `SNESGetNPC()`, it will have
299: its parent's Gauss-Seidel routine associated with it.
301: By default this routine computes the solution norm at each iteration, this can be time consuming, you can turn this off with `SNESSetNormSchedule()`
302: or -snes_norm_schedule none
304: References:
305: . * - Peter R. Brune, Matthew G. Knepley, Barry F. Smith, and Xuemin Tu, "Composing Scalable Nonlinear Algebraic Solvers",
306: SIAM Review, 57(4), 2015
308: .seealso: `SNESNCG`, `SNESCreate()`, `SNES`, `SNESSetType()`, `SNESSetNGS()`, `SNESType`, `SNESNGSSetSweeps()`, `SNESNGSSetTolerances()`,
309: `SNESSetNormSchedule()`
310: M*/
312: PETSC_EXTERN PetscErrorCode SNESCreate_NGS(SNES snes)
313: {
314: SNES_NGS *gs;
316: PetscFunctionBegin;
317: snes->ops->destroy = SNESDestroy_NGS;
318: snes->ops->setup = SNESSetUp_NGS;
319: snes->ops->setfromoptions = SNESSetFromOptions_NGS;
320: snes->ops->view = SNESView_NGS;
321: snes->ops->solve = SNESSolve_NGS;
322: snes->ops->reset = SNESReset_NGS;
324: snes->usesksp = PETSC_FALSE;
325: snes->usesnpc = PETSC_FALSE;
327: snes->alwayscomputesfinalresidual = PETSC_FALSE;
329: if (!snes->tolerancesset) {
330: snes->max_its = 10000;
331: snes->max_funcs = 10000;
332: }
334: PetscCall(PetscNew(&gs));
336: gs->sweeps = 1;
337: gs->rtol = 1e-5;
338: gs->abstol = PETSC_MACHINE_EPSILON;
339: gs->stol = 1000 * PETSC_MACHINE_EPSILON;
340: gs->max_its = 50;
341: gs->h = PETSC_SQRT_MACHINE_EPSILON;
343: snes->data = (void *)gs;
344: PetscFunctionReturn(PETSC_SUCCESS);
345: }