Actual source code: rich.c

petsc-master 2019-10-17
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  2: /*
  3:             This implements Richardson Iteration.
  4: */
  5:  #include <../src/ksp/ksp/impls/rich/richardsonimpl.h>

  7: PetscErrorCode KSPSetUp_Richardson(KSP ksp)
  8: {
 10:   KSP_Richardson *richardsonP = (KSP_Richardson*)ksp->data;

 13:   if (richardsonP->selfscale) {
 14:     KSPSetWorkVecs(ksp,4);
 15:   } else {
 16:     KSPSetWorkVecs(ksp,2);
 17:   }
 18:   return(0);
 19: }

 21: PetscErrorCode  KSPSolve_Richardson(KSP ksp)
 22: {
 24:   PetscInt       i,maxit;
 25:   PetscReal      rnorm = 0.0,abr;
 26:   PetscScalar    scale,rdot;
 27:   Vec            x,b,r,z,w = NULL,y = NULL;
 28:   PetscInt       xs, ws;
 29:   Mat            Amat,Pmat;
 30:   KSP_Richardson *richardsonP = (KSP_Richardson*)ksp->data;
 31:   PetscBool      exists,diagonalscale;
 32:   MatNullSpace   nullsp;

 35:   PCGetDiagonalScale(ksp->pc,&diagonalscale);
 36:   if (diagonalscale) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"Krylov method %s does not support diagonal scaling",((PetscObject)ksp)->type_name);

 38:   ksp->its = 0;

 40:   PCGetOperators(ksp->pc,&Amat,&Pmat);
 41:   x    = ksp->vec_sol;
 42:   b    = ksp->vec_rhs;
 43:   VecGetSize(x,&xs);
 44:   VecGetSize(ksp->work[0],&ws);
 45:   if (xs != ws) {
 46:     if (richardsonP->selfscale) {
 47:       KSPSetWorkVecs(ksp,4);
 48:     } else {
 49:       KSPSetWorkVecs(ksp,2);
 50:     }
 51:   }
 52:   r = ksp->work[0];
 53:   z = ksp->work[1];
 54:   if (richardsonP->selfscale) {
 55:     w = ksp->work[2];
 56:     y = ksp->work[3];
 57:   }
 58:   maxit = ksp->max_it;

 60:   /* if user has provided fast Richardson code use that */
 61:   PCApplyRichardsonExists(ksp->pc,&exists);
 62:   MatGetNullSpace(Pmat,&nullsp);
 63:   if (exists && maxit > 0 && richardsonP->scale == 1.0 && !ksp->numbermonitors && !ksp->transpose_solve && !nullsp) {
 64:     PCRichardsonConvergedReason reason;
 65:     PCApplyRichardson(ksp->pc,b,x,r,ksp->rtol,ksp->abstol,ksp->divtol,maxit,ksp->guess_zero,&ksp->its,&reason);
 66:     ksp->reason = (KSPConvergedReason)reason;
 67:     return(0);
 68:   } else if (exists && maxit > 0 && !ksp->numbermonitors && !ksp->transpose_solve && !nullsp) {
 69:     PetscInfo(ksp,"KSPSolve_Richardson: Warning, skipping optimized PCApplyRichardson() because scale factor is not 1.0\n");
 70:   }

 72:   if (!ksp->guess_zero) {                          /*   r <- b - A x     */
 73:     KSP_MatMult(ksp,Amat,x,r);
 74:     VecAYPX(r,-1.0,b);
 75:   } else {
 76:     VecCopy(b,r);
 77:   }

 79:   ksp->its = 0;
 80:   if (richardsonP->selfscale) {
 81:     KSP_PCApply(ksp,r,z);         /*   z <- B r          */
 82:     for (i=0; i<maxit; i++) {

 84:       if (ksp->normtype == KSP_NORM_UNPRECONDITIONED) {
 85:         VecNorm(r,NORM_2,&rnorm); /*   rnorm <- r'*r     */
 86:         KSPCheckNorm(ksp,rnorm);
 87:         KSPMonitor(ksp,i,rnorm);
 88:         ksp->rnorm = rnorm;
 89:         KSPLogResidualHistory(ksp,rnorm);
 90:         (*ksp->converged)(ksp,i,rnorm,&ksp->reason,ksp->cnvP);
 91:         if (ksp->reason) break;
 92:       } else if (ksp->normtype == KSP_NORM_PRECONDITIONED) {
 93:         VecNorm(z,NORM_2,&rnorm); /*   rnorm <- z'*z     */
 94:         KSPCheckNorm(ksp,rnorm);
 95:         KSPMonitor(ksp,i,rnorm);
 96:         ksp->rnorm = rnorm;
 97:         KSPLogResidualHistory(ksp,rnorm);
 98:         (*ksp->converged)(ksp,i,rnorm,&ksp->reason,ksp->cnvP);
 99:         if (ksp->reason) break;
100:       }
101:       KSP_PCApplyBAorAB(ksp,z,y,w); /* y = BAz = BABr */
102:       VecDotNorm2(z,y,&rdot,&abr);   /*   rdot = (Br)^T(BABR); abr = (BABr)^T (BABr) */
103:       scale = rdot/abr;
104:       PetscInfo1(ksp,"Self-scale factor %g\n",(double)PetscRealPart(scale));
105:       VecAXPY(x,scale,z);   /*   x  <- x + scale z */
106:       VecAXPY(r,-scale,w);  /*  r <- r - scale*Az */
107:       VecAXPY(z,-scale,y);  /*  z <- z - scale*y */
108:       ksp->its++;
109:     }
110:   } else {
111:     for (i=0; i<maxit; i++) {

113:       if (ksp->normtype == KSP_NORM_UNPRECONDITIONED) {
114:         VecNorm(r,NORM_2,&rnorm); /*   rnorm <- r'*r     */
115:         KSPCheckNorm(ksp,rnorm);
116:         KSPMonitor(ksp,i,rnorm);
117:         ksp->rnorm = rnorm;
118:         KSPLogResidualHistory(ksp,rnorm);
119:         (*ksp->converged)(ksp,i,rnorm,&ksp->reason,ksp->cnvP);
120:         if (ksp->reason) break;
121:       }

123:       KSP_PCApply(ksp,r,z);    /*   z <- B r          */

125:       if (ksp->normtype == KSP_NORM_PRECONDITIONED) {
126:         VecNorm(z,NORM_2,&rnorm); /*   rnorm <- z'*z     */
127:         KSPCheckNorm(ksp,rnorm);
128:         KSPMonitor(ksp,i,rnorm);
129:         ksp->rnorm = rnorm;
130:         KSPLogResidualHistory(ksp,rnorm);
131:         (*ksp->converged)(ksp,i,rnorm,&ksp->reason,ksp->cnvP);
132:         if (ksp->reason) break;
133:       }

135:       VecAXPY(x,richardsonP->scale,z);    /*   x  <- x + scale z */
136:       ksp->its++;

138:       if (i+1 < maxit || ksp->normtype != KSP_NORM_NONE) {
139:         KSP_MatMult(ksp,Amat,x,r);      /*   r  <- b - Ax      */
140:         VecAYPX(r,-1.0,b);
141:       }
142:     }
143:   }
144:   if (!ksp->reason) {
145:     if (ksp->normtype != KSP_NORM_NONE) {
146:       if (ksp->normtype == KSP_NORM_UNPRECONDITIONED) {
147:         VecNorm(r,NORM_2,&rnorm);     /*   rnorm <- r'*r     */
148:       } else {
149:         KSP_PCApply(ksp,r,z);   /*   z <- B r          */
150:         VecNorm(z,NORM_2,&rnorm);     /*   rnorm <- z'*z     */
151:       }
152:       KSPCheckNorm(ksp,rnorm);
153:       ksp->rnorm = rnorm;
154:       KSPLogResidualHistory(ksp,rnorm);
155:       KSPMonitor(ksp,i,rnorm);
156:     }
157:     if (ksp->its >= ksp->max_it) {
158:       if (ksp->normtype != KSP_NORM_NONE) {
159:         (*ksp->converged)(ksp,i,rnorm,&ksp->reason,ksp->cnvP);
160:         if (!ksp->reason) ksp->reason = KSP_DIVERGED_ITS;
161:       } else {
162:         ksp->reason = KSP_CONVERGED_ITS;
163:       }
164:     }
165:   }
166:   return(0);
167: }

169: PetscErrorCode KSPView_Richardson(KSP ksp,PetscViewer viewer)
170: {
171:   KSP_Richardson *richardsonP = (KSP_Richardson*)ksp->data;
173:   PetscBool      iascii;

176:   PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&iascii);
177:   if (iascii) {
178:     if (richardsonP->selfscale) {
179:       PetscViewerASCIIPrintf(viewer,"  using self-scale best computed damping factor\n");
180:     } else {
181:       PetscViewerASCIIPrintf(viewer,"  damping factor=%g\n",(double)richardsonP->scale);
182:     }
183:   }
184:   return(0);
185: }

187: PetscErrorCode KSPSetFromOptions_Richardson(PetscOptionItems *PetscOptionsObject,KSP ksp)
188: {
189:   KSP_Richardson *rich = (KSP_Richardson*)ksp->data;
191:   PetscReal      tmp;
192:   PetscBool      flg,flg2;

195:   PetscOptionsHead(PetscOptionsObject,"KSP Richardson Options");
196:   PetscOptionsReal("-ksp_richardson_scale","damping factor","KSPRichardsonSetScale",rich->scale,&tmp,&flg);
197:   if (flg) { KSPRichardsonSetScale(ksp,tmp); }
198:   PetscOptionsBool("-ksp_richardson_self_scale","dynamically determine optimal damping factor","KSPRichardsonSetSelfScale",rich->selfscale,&flg2,&flg);
199:   if (flg) { KSPRichardsonSetSelfScale(ksp,flg2); }
200:   PetscOptionsTail();
201:   return(0);
202: }

204: PetscErrorCode KSPDestroy_Richardson(KSP ksp)
205: {

209:   PetscObjectComposeFunction((PetscObject)ksp,"KSPRichardsonSetScale_C",NULL);
210:   KSPDestroyDefault(ksp);
211:   return(0);
212: }

214: static PetscErrorCode  KSPRichardsonSetScale_Richardson(KSP ksp,PetscReal scale)
215: {
216:   KSP_Richardson *richardsonP;

219:   richardsonP        = (KSP_Richardson*)ksp->data;
220:   richardsonP->scale = scale;
221:   return(0);
222: }

224: static PetscErrorCode  KSPRichardsonSetSelfScale_Richardson(KSP ksp,PetscBool selfscale)
225: {
226:   KSP_Richardson *richardsonP;

229:   richardsonP            = (KSP_Richardson*)ksp->data;
230:   richardsonP->selfscale = selfscale;
231:   return(0);
232: }

234: /*MC
235:      KSPRICHARDSON - The preconditioned Richardson iterative method

237:    Options Database Keys:
238: .   -ksp_richardson_scale - damping factor on the correction (defaults to 1.0)

240:    Level: beginner

242:    Notes:
243:     x^{n+1} = x^{n} + scale*B(b - A x^{n})

245:           Here B is the application of the preconditioner

247:           This method often (usually) will not converge unless scale is very small.

249:    Notes:
250:     For some preconditioners, currently SOR, the convergence test is skipped to improve speed,
251:     thus it always iterates the maximum number of iterations you've selected. When -ksp_monitor
252:     (or any other monitor) is turned on, the norm is computed at each iteration and so the convergence test is run unless
253:     you specifically call KSPSetNormType(ksp,KSP_NORM_NONE);

255:          For some preconditioners, currently PCMG and PCHYPRE with BoomerAMG if -ksp_monitor (and also
256:     any other monitor) is not turned on then the convergence test is done by the preconditioner itself and
257:     so the solver may run more or fewer iterations then if -ksp_monitor is selected.

259:     Supports only left preconditioning

261:   References:
262: .  1. - L. F. Richardson, "The Approximate Arithmetical Solution by Finite Differences of Physical Problems Involving
263:    Differential Equations, with an Application to the Stresses in a Masonry Dam",
264:   Philosophical Transactions of the Royal Society of London. Series A,
265:   Containing Papers of a Mathematical or Physical Character, Vol. 210, 1911 (1911).

267: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP,
268:            KSPRichardsonSetScale()

270: M*/

272: PETSC_EXTERN PetscErrorCode KSPCreate_Richardson(KSP ksp)
273: {
275:   KSP_Richardson *richardsonP;

278:   PetscNewLog(ksp,&richardsonP);
279:   ksp->data = (void*)richardsonP;

281:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,3);
282:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_LEFT,2);
283:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,1);

285:   ksp->ops->setup          = KSPSetUp_Richardson;
286:   ksp->ops->solve          = KSPSolve_Richardson;
287:   ksp->ops->destroy        = KSPDestroy_Richardson;
288:   ksp->ops->buildsolution  = KSPBuildSolutionDefault;
289:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
290:   ksp->ops->view           = KSPView_Richardson;
291:   ksp->ops->setfromoptions = KSPSetFromOptions_Richardson;

293:   PetscObjectComposeFunction((PetscObject)ksp,"KSPRichardsonSetScale_C",KSPRichardsonSetScale_Richardson);
294:   PetscObjectComposeFunction((PetscObject)ksp,"KSPRichardsonSetSelfScale_C",KSPRichardsonSetSelfScale_Richardson);

296:   richardsonP->scale = 1.0;
297:   return(0);
298: }