Actual source code: ms.c

  1: #include <petsc/private/snesimpl.h>

  3: static SNESMSType SNESMSDefault = SNESMSM62;
  4: static PetscBool  SNESMSRegisterAllCalled;
  5: static PetscBool  SNESMSPackageInitialized;

  7: typedef struct _SNESMSTableau *SNESMSTableau;
  8: struct _SNESMSTableau {
  9:   char      *name;
 10:   PetscInt   nstages;    /* Number of stages */
 11:   PetscInt   nregisters; /* Number of registers */
 12:   PetscReal  stability;  /* Scaled stability region */
 13:   PetscReal *gamma;      /* Coefficients of 3S* method */
 14:   PetscReal *delta;      /* Coefficients of 3S* method */
 15:   PetscReal *betasub;    /* Subdiagonal of beta in Shu-Osher form */
 16: };

 18: typedef struct _SNESMSTableauLink *SNESMSTableauLink;
 19: struct _SNESMSTableauLink {
 20:   struct _SNESMSTableau tab;
 21:   SNESMSTableauLink     next;
 22: };
 23: static SNESMSTableauLink SNESMSTableauList;

 25: typedef struct {
 26:   SNESMSTableau tableau; /* Tableau in low-storage form */
 27:   PetscReal     damping; /* Damping parameter, like length of (pseudo) time step */
 28: } SNES_MS;

 30: /*@C
 31:   SNESMSRegisterAll - Registers all of the multi-stage methods in `SNESMS`

 33:   Logically Collective

 35:   Level: developer

 37: .seealso: [](ch_snes), `SNES`, `SNESMS`, `SNESMSRegisterDestroy()`
 38: @*/
 39: PetscErrorCode SNESMSRegisterAll(void)
 40: {
 41:   PetscFunctionBegin;
 42:   if (SNESMSRegisterAllCalled) PetscFunctionReturn(PETSC_SUCCESS);
 43:   SNESMSRegisterAllCalled = PETSC_TRUE;

 45:   {
 46:     PetscReal alpha[1] = {1.0};
 47:     PetscCall(SNESMSRegister(SNESMSEULER, 1, 1, 1.0, NULL, NULL, alpha));
 48:   }

 50:   {
 51:     PetscReal gamma[3][6] = {
 52:       {0.0000000000000000E+00, -7.0304722367110606E-01, -1.9836719667506464E-01, -1.6023843981863788E+00, 9.4483822882855284E-02,  -1.4204296130641869E-01},
 53:       {1.0000000000000000E+00, 1.1111025767083920E+00,  5.6150921583923230E-01,  7.4151723494934041E-01,  3.1714538168600587E-01,  4.6479276238548706E-01 },
 54:       {0.0000000000000000E+00, 0.0000000000000000E+00,  0.0000000000000000E+00,  6.7968174970583317E-01,  -4.1755042846051737E-03, -1.9115668129923846E-01}
 55:     };
 56:     PetscReal delta[6]   = {1.0000000000000000E+00, 5.3275427433201750E-01, 6.0143544663985238E-01, 4.5874077053842177E-01, 2.7544386906104651E-01, 0.0000000000000000E+00};
 57:     PetscReal betasub[6] = {8.4753115429481929E-01, 7.4018896368655618E-01, 6.5963574086583309E-03, 4.6747795645517759E-01, 1.3314545813643919E-01, 5.3260800028018784E-01};
 58:     PetscCall(SNESMSRegister(SNESMSM62, 6, 3, 1.0, &gamma[0][0], delta, betasub));
 59:   }

 61:   { /* Jameson (1983) */
 62:     PetscReal alpha[4] = {0.25, 0.5, 0.55, 1.0};
 63:     PetscCall(SNESMSRegister(SNESMSJAMESON83, 4, 1, 1.0, NULL, NULL, alpha));
 64:   }

 66:   { /* Van Leer, Tai, and Powell (1989) 1 stage, order 1 */
 67:     PetscReal alpha[1] = {1.0};
 68:     PetscCall(SNESMSRegister(SNESMSVLTP11, 1, 1, 0.5, NULL, NULL, alpha));
 69:   }
 70:   { /* Van Leer, Tai, and Powell (1989) 2 stage, order 1 */
 71:     PetscReal alpha[2] = {0.3333, 1.0};
 72:     PetscCall(SNESMSRegister(SNESMSVLTP21, 2, 1, 1.0, NULL, NULL, alpha));
 73:   }
 74:   { /* Van Leer, Tai, and Powell (1989) 3 stage, order 1 */
 75:     PetscReal alpha[3] = {0.1481, 0.4000, 1.0};
 76:     PetscCall(SNESMSRegister(SNESMSVLTP31, 3, 1, 1.5, NULL, NULL, alpha));
 77:   }
 78:   { /* Van Leer, Tai, and Powell (1989) 4 stage, order 1 */
 79:     PetscReal alpha[4] = {0.0833, 0.2069, 0.4265, 1.0};
 80:     PetscCall(SNESMSRegister(SNESMSVLTP41, 4, 1, 2.0, NULL, NULL, alpha));
 81:   }
 82:   { /* Van Leer, Tai, and Powell (1989) 5 stage, order 1 */
 83:     PetscReal alpha[5] = {0.0533, 0.1263, 0.2375, 0.4414, 1.0};
 84:     PetscCall(SNESMSRegister(SNESMSVLTP51, 5, 1, 2.5, NULL, NULL, alpha));
 85:   }
 86:   { /* Van Leer, Tai, and Powell (1989) 6 stage, order 1 */
 87:     PetscReal alpha[6] = {0.0370, 0.0851, 0.1521, 0.2562, 0.4512, 1.0};
 88:     PetscCall(SNESMSRegister(SNESMSVLTP61, 6, 1, 3.0, NULL, NULL, alpha));
 89:   }
 90:   PetscFunctionReturn(PETSC_SUCCESS);
 91: }

 93: /*@C
 94:   SNESMSRegisterDestroy - Frees the list of schemes that were registered by `SNESMSRegister()`.

 96:   Logically Collective

 98:   Level: developer

100: .seealso: [](ch_snes), `SNES`, `SNESMS`, `SNESMSRegister()`, `SNESMSRegisterAll()`
101: @*/
102: PetscErrorCode SNESMSRegisterDestroy(void)
103: {
104:   SNESMSTableauLink link;

106:   PetscFunctionBegin;
107:   while ((link = SNESMSTableauList)) {
108:     SNESMSTableau t   = &link->tab;
109:     SNESMSTableauList = link->next;

111:     PetscCall(PetscFree(t->name));
112:     PetscCall(PetscFree(t->gamma));
113:     PetscCall(PetscFree(t->delta));
114:     PetscCall(PetscFree(t->betasub));
115:     PetscCall(PetscFree(link));
116:   }
117:   SNESMSRegisterAllCalled = PETSC_FALSE;
118:   PetscFunctionReturn(PETSC_SUCCESS);
119: }

121: /*@C
122:   SNESMSInitializePackage - This function initializes everything in the `SNESMS` package. It is called
123:   from `SNESInitializePackage()`.

125:   Level: developer

127: .seealso: [](ch_snes), `SNES`, `SNESMS`, `SNESMSRegister()`, `SNESMSRegisterAll()`, `PetscInitialize()`
128: @*/
129: PetscErrorCode SNESMSInitializePackage(void)
130: {
131:   PetscFunctionBegin;
132:   if (SNESMSPackageInitialized) PetscFunctionReturn(PETSC_SUCCESS);
133:   SNESMSPackageInitialized = PETSC_TRUE;

135:   PetscCall(SNESMSRegisterAll());
136:   PetscCall(PetscRegisterFinalize(SNESMSFinalizePackage));
137:   PetscFunctionReturn(PETSC_SUCCESS);
138: }

140: /*@C
141:   SNESMSFinalizePackage - This function destroys everything in the `SNESMS` package. It is
142:   called from `PetscFinalize()`.

144:   Level: developer

146: .seealso: [](ch_snes), `SNES`, `SNESMS`, `SNESMSRegister()`, `SNESMSRegisterAll()`, `SNESMSInitializePackage()`, `PetscFinalize()`
147: @*/
148: PetscErrorCode SNESMSFinalizePackage(void)
149: {
150:   PetscFunctionBegin;
151:   SNESMSPackageInitialized = PETSC_FALSE;

153:   PetscCall(SNESMSRegisterDestroy());
154:   PetscFunctionReturn(PETSC_SUCCESS);
155: }

157: /*@C
158:   SNESMSRegister - register a multistage scheme for `SNESMS`

160:   Logically Collective

162:   Input Parameters:
163: + name       - identifier for method
164: . nstages    - number of stages
165: . nregisters - number of registers used by low-storage implementation
166: . stability  - scaled stability region
167: . gamma      - coefficients, see Ketcheson's paper {cite}`ketcheson2010runge`
168: . delta      - coefficients, see Ketcheson's paper {cite}`ketcheson2010runge`
169: - betasub    - subdiagonal of Shu-Osher form

171:   Level: advanced

173:   Notes:
174:   The notation is described in {cite}`ketcheson2010runge` Ketcheson (2010) Runge-Kutta methods with minimum storage implementations.

176:   Many multistage schemes are of the form

178:   $$
179:   \begin{align*}
180:   X_0 = X^{(n)} \\
181:   X_k = X_0 + \alpha_k * F(X_{k-1}), k = 1,\ldots,s \\
182:   X^{(n+1)} = X_s
183:   \end{align*}
184:   $$

186:   These methods can be registered with
187: .vb
188:    SNESMSRegister("name",s,1,stability,NULL,NULL,alpha);
189: .ve

191: .seealso: [](ch_snes), `SNES`, `SNESMS`
192: @*/
193: PetscErrorCode SNESMSRegister(SNESMSType name, PetscInt nstages, PetscInt nregisters, PetscReal stability, const PetscReal gamma[], const PetscReal delta[], const PetscReal betasub[])
194: {
195:   SNESMSTableauLink link;
196:   SNESMSTableau     t;

198:   PetscFunctionBegin;
199:   PetscAssertPointer(name, 1);
200:   PetscCheck(nstages >= 1, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Must have at least one stage");
201:   if (gamma || delta) {
202:     PetscCheck(nregisters == 3, PETSC_COMM_SELF, PETSC_ERR_SUP, "Only support for methods written in 3-register form");
203:     PetscAssertPointer(gamma, 5);
204:     PetscAssertPointer(delta, 6);
205:   } else {
206:     PetscCheck(nregisters == 1, PETSC_COMM_SELF, PETSC_ERR_SUP, "Only support for methods written in 1-register form");
207:   }
208:   PetscAssertPointer(betasub, 7);

210:   PetscCall(SNESMSInitializePackage());
211:   PetscCall(PetscNew(&link));
212:   t = &link->tab;
213:   PetscCall(PetscStrallocpy(name, &t->name));
214:   t->nstages    = nstages;
215:   t->nregisters = nregisters;
216:   t->stability  = stability;

218:   if (gamma && delta) {
219:     PetscCall(PetscMalloc1(nstages * nregisters, &t->gamma));
220:     PetscCall(PetscMalloc1(nstages, &t->delta));
221:     PetscCall(PetscArraycpy(t->gamma, gamma, nstages * nregisters));
222:     PetscCall(PetscArraycpy(t->delta, delta, nstages));
223:   }
224:   PetscCall(PetscMalloc1(nstages, &t->betasub));
225:   PetscCall(PetscArraycpy(t->betasub, betasub, nstages));

227:   link->next        = SNESMSTableauList;
228:   SNESMSTableauList = link;
229:   PetscFunctionReturn(PETSC_SUCCESS);
230: }

232: /*
233:   X - initial state, updated in-place.
234:   F - residual, computed at the initial X on input
235: */
236: static PetscErrorCode SNESMSStep_3Sstar(SNES snes, Vec X, Vec F)
237: {
238:   SNES_MS         *ms      = (SNES_MS *)snes->data;
239:   SNESMSTableau    t       = ms->tableau;
240:   const PetscInt   nstages = t->nstages;
241:   const PetscReal *gamma = t->gamma, *delta = t->delta, *betasub = t->betasub;
242:   Vec              S1 = X, S2 = snes->work[1], S3 = snes->work[2], Y = snes->work[0], S1copy = snes->work[3];

244:   PetscFunctionBegin;
245:   PetscCall(VecZeroEntries(S2));
246:   PetscCall(VecCopy(X, S3));
247:   for (PetscInt i = 0; i < nstages; i++) {
248:     Vec               Ss[]     = {S1copy, S2, S3, Y};
249:     const PetscScalar scoeff[] = {gamma[0 * nstages + i] - 1, gamma[1 * nstages + i], gamma[2 * nstages + i], -betasub[i] * ms->damping};

251:     PetscCall(VecAXPY(S2, delta[i], S1));
252:     if (i > 0) PetscCall(SNESComputeFunction(snes, S1, F));
253:     PetscCall(KSPSolve(snes->ksp, F, Y));
254:     PetscCall(VecCopy(S1, S1copy));
255:     PetscCall(VecMAXPY(S1, 4, scoeff, Ss));
256:   }
257:   PetscFunctionReturn(PETSC_SUCCESS);
258: }

260: /*
261:   X - initial state, updated in-place.
262:   F - residual, computed at the initial X on input
263: */
264: static PetscErrorCode SNESMSStep_Basic(SNES snes, Vec X, Vec F)
265: {
266:   SNES_MS         *ms    = (SNES_MS *)snes->data;
267:   SNESMSTableau    tab   = ms->tableau;
268:   const PetscReal *alpha = tab->betasub, h = ms->damping;
269:   PetscInt         i, nstages              = tab->nstages;
270:   Vec              X0 = snes->work[0];

272:   PetscFunctionBegin;
273:   PetscCall(VecCopy(X, X0));
274:   for (i = 0; i < nstages; i++) {
275:     if (i > 0) PetscCall(SNESComputeFunction(snes, X, F));
276:     PetscCall(KSPSolve(snes->ksp, F, X));
277:     PetscCall(VecAYPX(X, -alpha[i] * h, X0));
278:   }
279:   PetscFunctionReturn(PETSC_SUCCESS);
280: }

282: static PetscErrorCode SNESMSStep_Step(SNES snes, Vec X, Vec F)
283: {
284:   SNES_MS      *ms  = (SNES_MS *)snes->data;
285:   SNESMSTableau tab = ms->tableau;

287:   PetscFunctionBegin;
288:   if (tab->gamma && tab->delta) {
289:     PetscCall(SNESMSStep_3Sstar(snes, X, F));
290:   } else {
291:     PetscCall(SNESMSStep_Basic(snes, X, F));
292:   }
293:   PetscFunctionReturn(PETSC_SUCCESS);
294: }

296: static PetscErrorCode SNESMSStep_Norms(SNES snes, PetscInt iter, Vec F)
297: {
298:   PetscReal fnorm;

300:   PetscFunctionBegin;
301:   if (SNESNeedNorm_Private(snes, iter)) {
302:     PetscCall(VecNorm(F, NORM_2, &fnorm)); /* fnorm <- ||F||  */
303:     SNESCheckFunctionNorm(snes, fnorm);
304:     /* Monitor convergence */
305:     PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
306:     snes->iter = iter;
307:     snes->norm = fnorm;
308:     PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
309:     PetscCall(SNESLogConvergenceHistory(snes, snes->norm, 0));
310:     /* Test for convergence */
311:     PetscCall(SNESConverged(snes, snes->iter, 0.0, 0.0, fnorm));
312:     PetscCall(SNESMonitor(snes, snes->iter, snes->norm));
313:   } else if (iter > 0) {
314:     PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
315:     snes->iter = iter;
316:     PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
317:   }
318:   PetscFunctionReturn(PETSC_SUCCESS);
319: }

321: static PetscErrorCode SNESSolve_MS(SNES snes)
322: {
323:   Vec      X = snes->vec_sol, F = snes->vec_func;
324:   PetscInt i;

326:   PetscFunctionBegin;
327:   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);
328:   PetscCall(PetscCitationsRegister(SNESCitation, &SNEScite));

330:   snes->reason = SNES_CONVERGED_ITERATING;
331:   PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
332:   snes->iter = 0;
333:   snes->norm = 0;
334:   PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));

336:   if (!snes->vec_func_init_set) {
337:     PetscCall(SNESComputeFunction(snes, X, F));
338:   } else snes->vec_func_init_set = PETSC_FALSE;

340:   PetscCall(SNESMSStep_Norms(snes, 0, F));
341:   if (snes->reason) PetscFunctionReturn(PETSC_SUCCESS);

343:   for (i = 0; i < snes->max_its; i++) {
344:     /* Call general purpose update function */
345:     PetscTryTypeMethod(snes, update, snes->iter);

347:     if (i == 0 && snes->jacobian) {
348:       /* This method does not require a Jacobian, but it is usually preconditioned by PBJacobi */
349:       PetscCall(SNESComputeJacobian(snes, snes->vec_sol, snes->jacobian, snes->jacobian_pre));
350:       SNESCheckJacobianDomainerror(snes);
351:       PetscCall(KSPSetOperators(snes->ksp, snes->jacobian, snes->jacobian_pre));
352:     }

354:     PetscCall(SNESMSStep_Step(snes, X, F));

356:     if (i < snes->max_its - 1 || SNESNeedNorm_Private(snes, i + 1)) PetscCall(SNESComputeFunction(snes, X, F));

358:     PetscCall(SNESMSStep_Norms(snes, i + 1, F));
359:     if (snes->reason) PetscFunctionReturn(PETSC_SUCCESS);
360:   }
361:   PetscFunctionReturn(PETSC_SUCCESS);
362: }

364: static PetscErrorCode SNESSetUp_MS(SNES snes)
365: {
366:   SNES_MS      *ms    = (SNES_MS *)snes->data;
367:   SNESMSTableau tab   = ms->tableau;
368:   PetscInt      nwork = tab->nregisters + 1; // +1 because VecMAXPY() in SNESMSStep_3Sstar()
369:                                              // needs an extra work vec

371:   PetscFunctionBegin;
372:   PetscCall(SNESSetWorkVecs(snes, nwork));
373:   PetscCall(SNESSetUpMatrices(snes));
374:   PetscFunctionReturn(PETSC_SUCCESS);
375: }

377: static PetscErrorCode SNESReset_MS(SNES snes)
378: {
379:   PetscFunctionBegin;
380:   PetscFunctionReturn(PETSC_SUCCESS);
381: }

383: static PetscErrorCode SNESDestroy_MS(SNES snes)
384: {
385:   PetscFunctionBegin;
386:   PetscCall(SNESReset_MS(snes));
387:   PetscCall(PetscFree(snes->data));
388:   PetscCall(PetscObjectComposeFunction((PetscObject)snes, "SNESMSGetType_C", NULL));
389:   PetscCall(PetscObjectComposeFunction((PetscObject)snes, "SNESMSSetType_C", NULL));
390:   PetscCall(PetscObjectComposeFunction((PetscObject)snes, "SNESMSGetDamping_C", NULL));
391:   PetscCall(PetscObjectComposeFunction((PetscObject)snes, "SNESMSSetDamping_C", NULL));
392:   PetscFunctionReturn(PETSC_SUCCESS);
393: }

395: static PetscErrorCode SNESView_MS(SNES snes, PetscViewer viewer)
396: {
397:   PetscBool     iascii;
398:   SNES_MS      *ms  = (SNES_MS *)snes->data;
399:   SNESMSTableau tab = ms->tableau;

401:   PetscFunctionBegin;
402:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &iascii));
403:   if (iascii) PetscCall(PetscViewerASCIIPrintf(viewer, "  multi-stage method type: %s\n", tab->name));
404:   PetscFunctionReturn(PETSC_SUCCESS);
405: }

407: static PetscErrorCode SNESSetFromOptions_MS(SNES snes, PetscOptionItems *PetscOptionsObject)
408: {
409:   PetscFunctionBegin;
410:   PetscOptionsHeadBegin(PetscOptionsObject, "SNES MS options");
411:   {
412:     SNESMSTableauLink link;
413:     PetscInt          count, choice;
414:     PetscBool         flg;
415:     const char      **namelist;
416:     SNESMSType        mstype;
417:     PetscReal         damping;
418:     PetscBool         norms = PETSC_FALSE;

420:     PetscCall(SNESMSGetType(snes, &mstype));
421:     for (link = SNESMSTableauList, count = 0; link; link = link->next, count++)
422:       ;
423:     PetscCall(PetscMalloc1(count, (char ***)&namelist));
424:     for (link = SNESMSTableauList, count = 0; link; link = link->next, count++) namelist[count] = link->tab.name;
425:     PetscCall(PetscOptionsEList("-snes_ms_type", "Multistage smoother type", "SNESMSSetType", (const char *const *)namelist, count, mstype, &choice, &flg));
426:     if (flg) PetscCall(SNESMSSetType(snes, namelist[choice]));
427:     PetscCall(PetscFree(namelist));
428:     PetscCall(SNESMSGetDamping(snes, &damping));
429:     PetscCall(PetscOptionsReal("-snes_ms_damping", "Damping for multistage method", "SNESMSSetDamping", damping, &damping, &flg));
430:     if (flg) PetscCall(SNESMSSetDamping(snes, damping));

432:     /* deprecated option */
433:     PetscCall(PetscOptionsDeprecated("-snes_ms_norms", NULL, "3.20", "Use -snes_norm_schedule always"));
434:     PetscCall(PetscOptionsBool("-snes_ms_norms", NULL, NULL, norms, &norms, NULL));
435:     if (norms) PetscCall(SNESSetNormSchedule(snes, SNES_NORM_ALWAYS));
436:   }
437:   PetscOptionsHeadEnd();
438:   PetscFunctionReturn(PETSC_SUCCESS);
439: }

441: static PetscErrorCode SNESMSGetType_MS(SNES snes, SNESMSType *mstype)
442: {
443:   SNES_MS      *ms  = (SNES_MS *)snes->data;
444:   SNESMSTableau tab = ms->tableau;

446:   PetscFunctionBegin;
447:   *mstype = tab->name;
448:   PetscFunctionReturn(PETSC_SUCCESS);
449: }

451: static PetscErrorCode SNESMSSetType_MS(SNES snes, SNESMSType mstype)
452: {
453:   SNES_MS          *ms = (SNES_MS *)snes->data;
454:   SNESMSTableauLink link;
455:   PetscBool         match;

457:   PetscFunctionBegin;
458:   if (ms->tableau) {
459:     PetscCall(PetscStrcmp(ms->tableau->name, mstype, &match));
460:     if (match) PetscFunctionReturn(PETSC_SUCCESS);
461:   }
462:   for (link = SNESMSTableauList; link; link = link->next) {
463:     PetscCall(PetscStrcmp(link->tab.name, mstype, &match));
464:     if (match) {
465:       if (snes->setupcalled) PetscCall(SNESReset_MS(snes));
466:       ms->tableau = &link->tab;
467:       if (snes->setupcalled) PetscCall(SNESSetUp_MS(snes));
468:       PetscFunctionReturn(PETSC_SUCCESS);
469:     }
470:   }
471:   SETERRQ(PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_UNKNOWN_TYPE, "Could not find '%s'", mstype);
472: }

474: /*@C
475:   SNESMSGetType - Get the type of multistage smoother `SNESMS`

477:   Not Collective

479:   Input Parameter:
480: . snes - nonlinear solver context

482:   Output Parameter:
483: . mstype - type of multistage method

485:   Level: advanced

487: .seealso: [](ch_snes), `SNESMS`, `SNESMSSetType()`, `SNESMSType`
488: @*/
489: PetscErrorCode SNESMSGetType(SNES snes, SNESMSType *mstype)
490: {
491:   PetscFunctionBegin;
493:   PetscAssertPointer(mstype, 2);
494:   PetscUseMethod(snes, "SNESMSGetType_C", (SNES, SNESMSType *), (snes, mstype));
495:   PetscFunctionReturn(PETSC_SUCCESS);
496: }

498: /*@C
499:   SNESMSSetType - Set the type of multistage smoother `SNESMS`

501:   Logically Collective

503:   Input Parameters:
504: + snes   - nonlinear solver context
505: - mstype - type of multistage method

507:   Level: advanced

509: .seealso: [](ch_snes), `SNESMS`, `SNESMSGetType()`, `SNESMSType`
510: @*/
511: PetscErrorCode SNESMSSetType(SNES snes, SNESMSType mstype)
512: {
513:   PetscFunctionBegin;
515:   PetscAssertPointer(mstype, 2);
516:   PetscTryMethod(snes, "SNESMSSetType_C", (SNES, SNESMSType), (snes, mstype));
517:   PetscFunctionReturn(PETSC_SUCCESS);
518: }

520: static PetscErrorCode SNESMSGetDamping_MS(SNES snes, PetscReal *damping)
521: {
522:   SNES_MS *ms = (SNES_MS *)snes->data;

524:   PetscFunctionBegin;
525:   *damping = ms->damping;
526:   PetscFunctionReturn(PETSC_SUCCESS);
527: }

529: static PetscErrorCode SNESMSSetDamping_MS(SNES snes, PetscReal damping)
530: {
531:   SNES_MS *ms = (SNES_MS *)snes->data;

533:   PetscFunctionBegin;
534:   ms->damping = damping;
535:   PetscFunctionReturn(PETSC_SUCCESS);
536: }

538: /*@C
539:   SNESMSGetDamping - Get the damping parameter of `SNESMS` multistage scheme

541:   Not Collective

543:   Input Parameter:
544: . snes - nonlinear solver context

546:   Output Parameter:
547: . damping - damping parameter

549:   Level: advanced

551: .seealso: [](ch_snes), `SNESMSSetDamping()`, `SNESMS`
552: @*/
553: PetscErrorCode SNESMSGetDamping(SNES snes, PetscReal *damping)
554: {
555:   PetscFunctionBegin;
557:   PetscAssertPointer(damping, 2);
558:   PetscUseMethod(snes, "SNESMSGetDamping_C", (SNES, PetscReal *), (snes, damping));
559:   PetscFunctionReturn(PETSC_SUCCESS);
560: }

562: /*@C
563:   SNESMSSetDamping - Set the damping parameter for a `SNESMS` multistage scheme

565:   Logically Collective

567:   Input Parameters:
568: + snes    - nonlinear solver context
569: - damping - damping parameter

571:   Level: advanced

573: .seealso: [](ch_snes), `SNESMSGetDamping()`, `SNESMS`
574: @*/
575: PetscErrorCode SNESMSSetDamping(SNES snes, PetscReal damping)
576: {
577:   PetscFunctionBegin;
580:   PetscTryMethod(snes, "SNESMSSetDamping_C", (SNES, PetscReal), (snes, damping));
581:   PetscFunctionReturn(PETSC_SUCCESS);
582: }

584: /*MC
585:       SNESMS - multi-stage smoothers

587:       Options Database Keys:
588: +     -snes_ms_type    - type of multi-stage smoother
589: -     -snes_ms_damping - damping for multi-stage method

591:       Level: advanced

593:       Notes:
594:       These multistage methods are explicit Runge-Kutta methods that are often used as smoothers for
595:       FAS multigrid for transport problems. In the linear case, these are equivalent to polynomial smoothers (such as Chebyshev).

597:       Multi-stage smoothers should usually be preconditioned by point-block Jacobi to ensure proper scaling and to normalize the wave speeds.

599:       The methods are specified in low storage form (Ketcheson 2010). New methods can be registered with `SNESMSRegister()`.

601:       See {cite}`ketcheson2010runge`, {cite}`jameson1983`, {cite}`pierce1997preconditioned`, and {cite}`va1981design`

603: .seealso: [](ch_snes), `SNESCreate()`, `SNES`, `SNESSetType()`, `SNESMS`, `SNESFAS`, `KSPCHEBYSHEV`, `SNESMSSetDamping()`, `SNESMSGetDamping()`,
604:           `SNESMSSetType()`, `SNESMSGetType()`
605: M*/

607: PETSC_EXTERN PetscErrorCode SNESCreate_MS(SNES snes)
608: {
609:   SNES_MS *ms;

611:   PetscFunctionBegin;
612:   PetscCall(SNESMSInitializePackage());

614:   snes->ops->setup          = SNESSetUp_MS;
615:   snes->ops->solve          = SNESSolve_MS;
616:   snes->ops->destroy        = SNESDestroy_MS;
617:   snes->ops->setfromoptions = SNESSetFromOptions_MS;
618:   snes->ops->view           = SNESView_MS;
619:   snes->ops->reset          = SNESReset_MS;

621:   snes->usesnpc = PETSC_FALSE;
622:   snes->usesksp = PETSC_TRUE;

624:   snes->alwayscomputesfinalresidual = PETSC_FALSE;

626:   PetscCall(PetscNew(&ms));
627:   snes->data  = (void *)ms;
628:   ms->damping = 0.9;

630:   PetscCall(PetscObjectComposeFunction((PetscObject)snes, "SNESMSGetType_C", SNESMSGetType_MS));
631:   PetscCall(PetscObjectComposeFunction((PetscObject)snes, "SNESMSSetType_C", SNESMSSetType_MS));
632:   PetscCall(PetscObjectComposeFunction((PetscObject)snes, "SNESMSGetDamping_C", SNESMSGetDamping_MS));
633:   PetscCall(PetscObjectComposeFunction((PetscObject)snes, "SNESMSSetDamping_C", SNESMSSetDamping_MS));

635:   PetscCall(SNESMSSetType(snes, SNESMSDefault));
636:   PetscFunctionReturn(PETSC_SUCCESS);
637: }