Actual source code: snesrichardson.c

petsc-3.6.1 2015-07-22
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  1: #include <../src/snes/impls/richardson/snesrichardsonimpl.h>


  6: PetscErrorCode SNESReset_NRichardson(SNES snes)
  7: {
  9:   return(0);
 10: }

 12: /*
 13:   SNESDestroy_NRichardson - Destroys the private SNES_NRichardson context that was created with SNESCreate_NRichardson().

 15:   Input Parameter:
 16: . snes - the SNES context

 18:   Application Interface Routine: SNESDestroy()
 19: */
 22: PetscErrorCode SNESDestroy_NRichardson(SNES snes)
 23: {

 27:   SNESReset_NRichardson(snes);
 28:   PetscFree(snes->data);
 29:   return(0);
 30: }

 32: /*
 33:    SNESSetUp_NRichardson - Sets up the internal data structures for the later use
 34:    of the SNESNRICHARDSON nonlinear solver.

 36:    Input Parameters:
 37: +  snes - the SNES context
 38: -  x - the solution vector

 40:    Application Interface Routine: SNESSetUp()
 41:  */
 44: PetscErrorCode SNESSetUp_NRichardson(SNES snes)
 45: {
 47:   if (snes->pcside == PC_RIGHT) {SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"NRichardson only supports left preconditioning");}
 48:   if (snes->functype == SNES_FUNCTION_DEFAULT) snes->functype = SNES_FUNCTION_UNPRECONDITIONED;
 49:   return(0);
 50: }

 52: /*
 53:   SNESSetFromOptions_NRichardson - Sets various parameters for the SNESNEWTONLS method.

 55:   Input Parameter:
 56: . snes - the SNES context

 58:   Application Interface Routine: SNESSetFromOptions()
 59: */
 62: static PetscErrorCode SNESSetFromOptions_NRichardson(PetscOptions *PetscOptionsObject,SNES snes)
 63: {
 65:   SNESLineSearch linesearch;

 68:   PetscOptionsHead(PetscOptionsObject,"SNES Richardson options");
 69:   PetscOptionsTail();
 70:   if (!snes->linesearch) {
 71:     SNESGetLineSearch(snes, &linesearch);
 72:     SNESLineSearchSetType(linesearch, SNESLINESEARCHL2);
 73:   }
 74:   return(0);
 75: }

 77: /*
 78:   SNESView_NRichardson - Prints info from the SNESRichardson data structure.

 80:   Input Parameters:
 81: + SNES - the SNES context
 82: - viewer - visualization context

 84:   Application Interface Routine: SNESView()
 85: */
 88: static PetscErrorCode SNESView_NRichardson(SNES snes, PetscViewer viewer)
 89: {
 90:   PetscBool      iascii;

 94:   PetscObjectTypeCompare((PetscObject) viewer, PETSCVIEWERASCII, &iascii);
 95:   if (iascii) {
 96:   }
 97:   return(0);
 98: }

100: /*
101:   SNESSolve_NRichardson - Solves a nonlinear system with the Richardson method.

103:   Input Parameters:
104: . snes - the SNES context

106:   Output Parameter:
107: . outits - number of iterations until termination

109:   Application Interface Routine: SNESSolve()
110: */
113: PetscErrorCode SNESSolve_NRichardson(SNES snes)
114: {
115:   Vec                  X, Y, F;
116:   PetscReal            xnorm, fnorm, ynorm;
117:   PetscInt             maxits, i;
118:   PetscErrorCode       ierr;
119:   SNESLineSearchReason lsresult;
120:   SNESConvergedReason  reason;


124:   if (snes->xl || snes->xu || snes->ops->computevariablebounds) {
125:     SETERRQ1(PetscObjectComm((PetscObject)snes),PETSC_ERR_ARG_WRONGSTATE, "SNES solver %s does not support bounds", ((PetscObject)snes)->type_name);
126:   }

128:   snes->reason = SNES_CONVERGED_ITERATING;

130:   maxits = snes->max_its;        /* maximum number of iterations */
131:   X      = snes->vec_sol;        /* X^n */
132:   Y      = snes->vec_sol_update; /* \tilde X */
133:   F      = snes->vec_func;       /* residual vector */

135:   PetscObjectSAWsTakeAccess((PetscObject)snes);
136:   snes->iter = 0;
137:   snes->norm = 0.;
138:   PetscObjectSAWsGrantAccess((PetscObject)snes);

140:   if (snes->pc && snes->functype == SNES_FUNCTION_PRECONDITIONED) {
141:     SNESApplyNPC(snes,X,NULL,F);
142:     SNESGetConvergedReason(snes->pc,&reason);
143:     if (reason < 0  && reason != SNES_DIVERGED_MAX_IT) {
144:       snes->reason = SNES_DIVERGED_INNER;
145:       return(0);
146:     }
147:     VecNorm(F,NORM_2,&fnorm);
148:   } else {
149:     if (!snes->vec_func_init_set) {
150:       SNESComputeFunction(snes,X,F);
151:     } else snes->vec_func_init_set = PETSC_FALSE;

153:     VecNorm(F,NORM_2,&fnorm);
154:     SNESCheckFunctionNorm(snes,fnorm);
155:   }
156:   if (snes->pc && snes->functype == SNES_FUNCTION_UNPRECONDITIONED) {
157:       SNESApplyNPC(snes,X,F,Y);
158:       SNESGetConvergedReason(snes->pc,&reason);
159:       if (reason < 0  && reason != SNES_DIVERGED_MAX_IT) {
160:         snes->reason = SNES_DIVERGED_INNER;
161:         return(0);
162:       }
163:   } else {
164:     VecCopy(F,Y);
165:   }

167:   PetscObjectSAWsTakeAccess((PetscObject)snes);
168:   snes->norm = fnorm;
169:   PetscObjectSAWsGrantAccess((PetscObject)snes);
170:   SNESLogConvergenceHistory(snes,fnorm,0);
171:   SNESMonitor(snes,0,fnorm);

173:   /* test convergence */
174:   (*snes->ops->converged)(snes,0,0.0,0.0,fnorm,&snes->reason,snes->cnvP);
175:   if (snes->reason) return(0);

177:   /* Call general purpose update function */
178:   if (snes->ops->update) {
179:     (*snes->ops->update)(snes, snes->iter);
180:   }

182:   /* set parameter for default relative tolerance convergence test */
183:   snes->ttol = fnorm*snes->rtol;
184:   /* test convergence */
185:   (*snes->ops->converged)(snes,0,0.0,0.0,fnorm,&snes->reason,snes->cnvP);
186:   if (snes->reason) return(0);

188:   for (i = 1; i < maxits+1; i++) {
189:     SNESLineSearchApply(snes->linesearch, X, F, &fnorm, Y);
190:     SNESLineSearchGetReason(snes->linesearch, &lsresult);
191:     SNESLineSearchGetNorms(snes->linesearch, &xnorm, &fnorm, &ynorm);
192:     if (lsresult) {
193:       if (++snes->numFailures >= snes->maxFailures) {
194:         snes->reason = SNES_DIVERGED_LINE_SEARCH;
195:         break;
196:       }
197:     }
198:     if (snes->nfuncs >= snes->max_funcs) {
199:       snes->reason = SNES_DIVERGED_FUNCTION_COUNT;
200:       break;
201:     }

203:     /* Monitor convergence */
204:     PetscObjectSAWsTakeAccess((PetscObject)snes);
205:     snes->iter = i;
206:     snes->norm = fnorm;
207:     PetscObjectSAWsGrantAccess((PetscObject)snes);
208:     SNESLogConvergenceHistory(snes,snes->norm,0);
209:     SNESMonitor(snes,snes->iter,snes->norm);
210:     /* Test for convergence */
211:     (*snes->ops->converged)(snes,snes->iter,xnorm,ynorm,fnorm,&snes->reason,snes->cnvP);
212:     if (snes->reason) break;

214:     /* Call general purpose update function */
215:     if (snes->ops->update) {
216:       (*snes->ops->update)(snes, snes->iter);
217:     }

219:     if (snes->pc) {
220:       if (snes->functype == SNES_FUNCTION_PRECONDITIONED) {
221:         SNESApplyNPC(snes,X,NULL,Y);
222:         VecNorm(F,NORM_2,&fnorm);
223:         VecCopy(Y,F);
224:       } else {
225:         SNESApplyNPC(snes,X,F,Y);
226:       }
227:       SNESGetConvergedReason(snes->pc,&reason);
228:       if (reason < 0  && reason != SNES_DIVERGED_MAX_IT) {
229:         snes->reason = SNES_DIVERGED_INNER;
230:         return(0);
231:       }
232:     } else {
233:       VecCopy(F,Y);
234:     }
235:   }
236:   if (i == maxits+1) {
237:     PetscInfo1(snes, "Maximum number of iterations has been reached: %D\n", maxits);
238:     if (!snes->reason) snes->reason = SNES_DIVERGED_MAX_IT;
239:   }
240:   return(0);
241: }

243: /*MC
244:   SNESNRICHARDSON - Richardson nonlinear solver that uses successive substitutions, also sometimes known as Picard iteration.

246:   Level: beginner

248:   Options Database:
249: +   -snes_linesearch_type <l2,cp,basic> Line search type.
250: -   -snes_linesearch_damping<1.0> Damping for the line search.

252:   Notes: If no inner nonlinear preconditioner is provided then solves F(x) - b = 0 using x^{n+1} = x^{n} - lambda
253:             (F(x^n) - b) where lambda is obtained either SNESLineSearchSetDamping(), -snes_damping or a line search.  If
254:             an inner nonlinear preconditioner is provided (either with -npc_snes_type or SNESSetNPC()) then the inner
255:             solver is called an initial solution x^n and the nonlinear Richardson uses x^{n+1} = x^{n} + lambda d^{n}
256:             where d^{n} = \hat{x}^{n} - x^{n} where \hat{x}^{n} is the solution returned from the inner solver.

258:             The update, especially without inner nonlinear preconditioner, may be ill-scaled.  If using the basic
259:             linesearch, one may have to scale the update with -snes_linesearch_damping

261:      This uses no derivative information thus will be much slower then Newton's method obtained with -snes_type ls

263: .seealso:  SNESCreate(), SNES, SNESSetType(), SNESNEWTONLS, SNESNEWTONTR, SNESNGMRES, SNESQN, SNESNCG
264: M*/
267: PETSC_EXTERN PetscErrorCode SNESCreate_NRichardson(SNES snes)
268: {
269:   PetscErrorCode   ierr;
270:   SNES_NRichardson *neP;

273:   snes->ops->destroy        = SNESDestroy_NRichardson;
274:   snes->ops->setup          = SNESSetUp_NRichardson;
275:   snes->ops->setfromoptions = SNESSetFromOptions_NRichardson;
276:   snes->ops->view           = SNESView_NRichardson;
277:   snes->ops->solve          = SNESSolve_NRichardson;
278:   snes->ops->reset          = SNESReset_NRichardson;

280:   snes->usesksp = PETSC_FALSE;
281:   snes->usespc  = PETSC_TRUE;

283:   snes->pcside = PC_LEFT;

285:   PetscNewLog(snes,&neP);
286:   snes->data = (void*) neP;

288:   if (!snes->tolerancesset) {
289:     snes->max_funcs = 30000;
290:     snes->max_its   = 10000;
291:     snes->stol      = 1e-20;
292:   }
293:   return(0);
294: }