Date: 2021-03-03T22:27:41+00:00

Actual source code: snesrichardson.c
petsc-3.14.5 2021-03-03
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      1: #include <../src/snes/impls/richardson/snesrichardsonimpl.h>

      4: PetscErrorCode SNESReset_NRichardson(SNES snes)
      5: {
      7:   return(0);
      8: }

     10: /*
     11:   SNESDestroy_NRichardson - Destroys the private SNES_NRichardson context that was created with SNESCreate_NRichardson().

     13:   Input Parameter:
     14: . snes - the SNES context

     16:   Application Interface Routine: SNESDestroy()
     17: */
     18: PetscErrorCode SNESDestroy_NRichardson(SNES snes)
     19: {

     23:   SNESReset_NRichardson(snes);
     24:   PetscFree(snes->data);
     25:   return(0);
     26: }

     28: /*
     29:    SNESSetUp_NRichardson - Sets up the internal data structures for the later use
     30:    of the SNESNRICHARDSON nonlinear solver.

     32:    Input Parameters:
     33: +  snes - the SNES context
     34: -  x - the solution vector

     36:    Application Interface Routine: SNESSetUp()
     37:  */
     38: PetscErrorCode SNESSetUp_NRichardson(SNES snes)
     39: {
     41:   if (snes->npcside== PC_RIGHT) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_WRONGSTATE,"NRichardson only supports left preconditioning");
     42:   if (snes->functype == SNES_FUNCTION_DEFAULT) snes->functype = SNES_FUNCTION_UNPRECONDITIONED;
     43:   return(0);
     44: }

     46: /*
     47:   SNESSetFromOptions_NRichardson - Sets various parameters for the SNESNEWTONLS method.

     49:   Input Parameter:
     50: . snes - the SNES context

     52:   Application Interface Routine: SNESSetFromOptions()
     53: */
     54: static PetscErrorCode SNESSetFromOptions_NRichardson(PetscOptionItems *PetscOptionsObject,SNES snes)
     55: {

     59:   PetscOptionsHead(PetscOptionsObject,"SNES Richardson options");
     60:   PetscOptionsTail();
     61:   return(0);
     62: }

     64: /*
     65:   SNESView_NRichardson - Prints info from the SNESRichardson data structure.

     67:   Input Parameters:
     68: + SNES - the SNES context
     69: - viewer - visualization context

     71:   Application Interface Routine: SNESView()
     72: */
     73: static PetscErrorCode SNESView_NRichardson(SNES snes, PetscViewer viewer)
     74: {
     75:   PetscBool      iascii;

     79:   PetscObjectTypeCompare((PetscObject) viewer, PETSCVIEWERASCII, &iascii);
     80:   if (iascii) {
     81:   }
     82:   return(0);
     83: }

     85: /*
     86:   SNESSolve_NRichardson - Solves a nonlinear system with the Richardson method.

     88:   Input Parameters:
     89: . snes - the SNES context

     91:   Output Parameter:
     92: . outits - number of iterations until termination

     94:   Application Interface Routine: SNESSolve()
     95: */
     96: PetscErrorCode SNESSolve_NRichardson(SNES snes)
     97: {
     98:   Vec                  X, Y, F;
     99:   PetscReal            xnorm, fnorm, ynorm;
    100:   PetscInt             maxits, i;
    101:   PetscErrorCode       ierr;
    102:   SNESLineSearchReason lsresult;
    103:   SNESConvergedReason  reason;

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

    108:   snes->reason = SNES_CONVERGED_ITERATING;

    110:   maxits = snes->max_its;        /* maximum number of iterations */
    111:   X      = snes->vec_sol;        /* X^n */
    112:   Y      = snes->vec_sol_update; /* \tilde X */
    113:   F      = snes->vec_func;       /* residual vector */

    115:   PetscObjectSAWsTakeAccess((PetscObject)snes);
    116:   snes->iter = 0;
    117:   snes->norm = 0.;
    118:   PetscObjectSAWsGrantAccess((PetscObject)snes);

    120:   if (snes->npc && snes->functype == SNES_FUNCTION_PRECONDITIONED) {
    121:     SNESApplyNPC(snes,X,NULL,F);
    122:     SNESGetConvergedReason(snes->npc,&reason);
    123:     if (reason < 0  && reason != SNES_DIVERGED_MAX_IT) {
    124:       snes->reason = SNES_DIVERGED_INNER;
    125:       return(0);
    126:     }
    127:     VecNorm(F,NORM_2,&fnorm);
    128:   } else {
    129:     if (!snes->vec_func_init_set) {
    130:       SNESComputeFunction(snes,X,F);
    131:     } else snes->vec_func_init_set = PETSC_FALSE;

    133:     VecNorm(F,NORM_2,&fnorm);
    134:     SNESCheckFunctionNorm(snes,fnorm);
    135:   }
    136:   if (snes->npc && snes->functype == SNES_FUNCTION_UNPRECONDITIONED) {
    137:       SNESApplyNPC(snes,X,F,Y);
    138:       SNESGetConvergedReason(snes->npc,&reason);
    139:       if (reason < 0  && reason != SNES_DIVERGED_MAX_IT) {
    140:         snes->reason = SNES_DIVERGED_INNER;
    141:         return(0);
    142:       }
    143:   } else {
    144:     VecCopy(F,Y);
    145:   }

    147:   PetscObjectSAWsTakeAccess((PetscObject)snes);
    148:   snes->norm = fnorm;
    149:   PetscObjectSAWsGrantAccess((PetscObject)snes);
    150:   SNESLogConvergenceHistory(snes,fnorm,0);
    151:   SNESMonitor(snes,0,fnorm);

    153:   /* test convergence */
    154:   (*snes->ops->converged)(snes,0,0.0,0.0,fnorm,&snes->reason,snes->cnvP);
    155:   if (snes->reason) return(0);

    157:   /* Call general purpose update function */
    158:   if (snes->ops->update) {
    159:     (*snes->ops->update)(snes, snes->iter);
    160:   }

    162:   /* set parameter for default relative tolerance convergence test */
    163:   snes->ttol = fnorm*snes->rtol;
    164:   /* test convergence */
    165:   (*snes->ops->converged)(snes,0,0.0,0.0,fnorm,&snes->reason,snes->cnvP);
    166:   if (snes->reason) return(0);

    168:   for (i = 1; i < maxits+1; i++) {
    169:     SNESLineSearchApply(snes->linesearch, X, F, &fnorm, Y);
    170:     SNESLineSearchGetReason(snes->linesearch, &lsresult);
    171:     SNESLineSearchGetNorms(snes->linesearch, &xnorm, &fnorm, &ynorm);
    172:     if (lsresult) {
    173:       if (++snes->numFailures >= snes->maxFailures) {
    174:         snes->reason = SNES_DIVERGED_LINE_SEARCH;
    175:         break;
    176:       }
    177:     }
    178:     if (snes->nfuncs >= snes->max_funcs && snes->max_funcs >= 0) {
    179:       snes->reason = SNES_DIVERGED_FUNCTION_COUNT;
    180:       break;
    181:     }

    183:     /* Monitor convergence */
    184:     PetscObjectSAWsTakeAccess((PetscObject)snes);
    185:     snes->iter = i;
    186:     snes->norm = fnorm;
    187:     snes->xnorm = xnorm;
    188:     snes->ynorm = ynorm;
    189:     PetscObjectSAWsGrantAccess((PetscObject)snes);
    190:     SNESLogConvergenceHistory(snes,snes->norm,0);
    191:     SNESMonitor(snes,snes->iter,snes->norm);
    192:     /* Test for convergence */
    193:     (*snes->ops->converged)(snes,snes->iter,xnorm,ynorm,fnorm,&snes->reason,snes->cnvP);
    194:     if (snes->reason) break;

    196:     /* Call general purpose update function */
    197:     if (snes->ops->update) {
    198:       (*snes->ops->update)(snes, snes->iter);
    199:     }

    201:     if (snes->npc) {
    202:       if (snes->functype == SNES_FUNCTION_PRECONDITIONED) {
    203:         SNESApplyNPC(snes,X,NULL,Y);
    204:         VecNorm(F,NORM_2,&fnorm);
    205:         VecCopy(Y,F);
    206:       } else {
    207:         SNESApplyNPC(snes,X,F,Y);
    208:       }
    209:       SNESGetConvergedReason(snes->npc,&reason);
    210:       if (reason < 0  && reason != SNES_DIVERGED_MAX_IT) {
    211:         snes->reason = SNES_DIVERGED_INNER;
    212:         return(0);
    213:       }
    214:     } else {
    215:       VecCopy(F,Y);
    216:     }
    217:   }
    218:   if (i == maxits+1) {
    219:     PetscInfo1(snes, "Maximum number of iterations has been reached: %D\n", maxits);
    220:     if (!snes->reason) snes->reason = SNES_DIVERGED_MAX_IT;
    221:   }
    222:   return(0);
    223: }

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

    228:   Level: beginner

    230:   Options Database:
    231: +   -snes_linesearch_type <l2,cp,basic> Line search type.
    232: -   -snes_linesearch_damping<1.0> Damping for the line search.

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

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

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

    246:      Only supports left non-linear preconditioning.

    248: .seealso:  SNESCreate(), SNES, SNESSetType(), SNESNEWTONLS, SNESNEWTONTR, SNESNGMRES, SNESQN, SNESNCG
    249: M*/
    250: PETSC_EXTERN PetscErrorCode SNESCreate_NRichardson(SNES snes)
    251: {
    252:   PetscErrorCode   ierr;
    253:   SNES_NRichardson *neP;
    254:   SNESLineSearch   linesearch;

    257:   snes->ops->destroy        = SNESDestroy_NRichardson;
    258:   snes->ops->setup          = SNESSetUp_NRichardson;
    259:   snes->ops->setfromoptions = SNESSetFromOptions_NRichardson;
    260:   snes->ops->view           = SNESView_NRichardson;
    261:   snes->ops->solve          = SNESSolve_NRichardson;
    262:   snes->ops->reset          = SNESReset_NRichardson;

    264:   snes->usesksp = PETSC_FALSE;
    265:   snes->usesnpc = PETSC_TRUE;

    267:   snes->npcside= PC_LEFT;

    269:   SNESGetLineSearch(snes, &linesearch);
    270:   if (!((PetscObject)linesearch)->type_name) {
    271:     SNESLineSearchSetType(linesearch, SNESLINESEARCHL2);
    272:   }

    274:   snes->alwayscomputesfinalresidual = PETSC_TRUE;

    276:   PetscNewLog(snes,&neP);
    277:   snes->data = (void*) neP;

    279:   if (!snes->tolerancesset) {
    280:     snes->max_funcs = 30000;
    281:     snes->max_its   = 10000;
    282:     snes->stol      = 1e-20;
    283:   }
    284:   return(0);
    285: }