Actual source code: rich.c

petsc-dev 2014-07-09
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  2: /*
  3:             This implements Richardson Iteration.
  4: */
  5: #include <petsc-private/kspimpl.h>              /*I "petscksp.h" I*/
  6: #include <../src/ksp/ksp/impls/rich/richardsonimpl.h>

 10: PetscErrorCode KSPSetUp_Richardson(KSP ksp)
 11: {
 13:   KSP_Richardson *richardsonP = (KSP_Richardson*)ksp->data;

 16:   if (richardsonP->selfscale) {
 17:     KSPSetWorkVecs(ksp,4);
 18:   } else {
 19:     KSPSetWorkVecs(ksp,2);
 20:   }
 21:   return(0);
 22: }

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

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

 42:   ksp->its = 0;

 44:   PCGetOperators(ksp->pc,&Amat,&Pmat);
 45:   x    = ksp->vec_sol;
 46:   b    = ksp->vec_rhs;
 47:   VecGetSize(x,&xs);
 48:   VecGetSize(ksp->work[0],&ws);
 49:   if (xs != ws) {
 50:     if (richardsonP->selfscale) {
 51:       KSPSetWorkVecs(ksp,4);
 52:     } else {
 53:       KSPSetWorkVecs(ksp,2);
 54:     }
 55:   }
 56:   r = ksp->work[0];
 57:   z = ksp->work[1];
 58:   if (richardsonP->selfscale) {
 59:     w = ksp->work[2];
 60:     y = ksp->work[3];
 61:   }
 62:   maxit = ksp->max_it;

 64:   /* if user has provided fast Richardson code use that */
 65:   PCApplyRichardsonExists(ksp->pc,&exists);
 66:   if (exists && !ksp->numbermonitors && !ksp->transpose_solve & !ksp->nullsp) {
 67:     PCRichardsonConvergedReason reason;
 68:     PCApplyRichardson(ksp->pc,b,x,r,ksp->rtol,ksp->abstol,ksp->divtol,maxit,ksp->guess_zero,&ksp->its,&reason);
 69:     ksp->reason = (KSPConvergedReason)reason;
 70:     return(0);
 71:   }

 73:   scale = richardsonP->scale;

 75:   if (!ksp->guess_zero) {                          /*   r <- b - A x     */
 76:     KSP_MatMult(ksp,Amat,x,r);
 77:     VecAYPX(r,-1.0,b);
 78:   } else {
 79:     VecCopy(b,r);
 80:   }

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

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

114:       if (ksp->normtype == KSP_NORM_UNPRECONDITIONED) {
115:         VecNorm(r,NORM_2,&rnorm); /*   rnorm <- r'*r     */
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:         KSPMonitor(ksp,i,rnorm);
128:         ksp->rnorm = rnorm;
129:         KSPLogResidualHistory(ksp,rnorm);
130:         (*ksp->converged)(ksp,i,rnorm,&ksp->reason,ksp->cnvP);
131:         if (ksp->reason) break;
132:       }

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

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

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,"  Richardson: using self-scale best computed damping factor\n");
180:     } else {
181:       PetscViewerASCIIPrintf(viewer,"  Richardson: damping factor=%g\n",(double)richardsonP->scale);
182:     }
183:   }
184:   return(0);
185: }

189: PetscErrorCode KSPSetFromOptions_Richardson(KSP ksp)
190: {
191:   KSP_Richardson *rich = (KSP_Richardson*)ksp->data;
193:   PetscReal      tmp;
194:   PetscBool      flg,flg2;

197:   PetscOptionsHead("KSP Richardson Options");
198:   PetscOptionsReal("-ksp_richardson_scale","damping factor","KSPRichardsonSetScale",rich->scale,&tmp,&flg);
199:   if (flg) { KSPRichardsonSetScale(ksp,tmp); }
200:   PetscOptionsBool("-ksp_richardson_self_scale","dynamically determine optimal damping factor","KSPRichardsonSetSelfScale",rich->selfscale,&flg2,&flg);
201:   if (flg) { KSPRichardsonSetSelfScale(ksp,flg2); }
202:   PetscOptionsTail();
203:   return(0);
204: }

208: PetscErrorCode KSPDestroy_Richardson(KSP ksp)
209: {

213:   PetscObjectComposeFunction((PetscObject)ksp,"KSPRichardsonSetScale_C",NULL);
214:   KSPDestroyDefault(ksp);
215:   return(0);
216: }

220: static PetscErrorCode  KSPRichardsonSetScale_Richardson(KSP ksp,PetscReal scale)
221: {
222:   KSP_Richardson *richardsonP;

225:   richardsonP        = (KSP_Richardson*)ksp->data;
226:   richardsonP->scale = scale;
227:   return(0);
228: }

232: static PetscErrorCode  KSPRichardsonSetSelfScale_Richardson(KSP ksp,PetscBool selfscale)
233: {
234:   KSP_Richardson *richardsonP;

237:   richardsonP            = (KSP_Richardson*)ksp->data;
238:   richardsonP->selfscale = selfscale;
239:   return(0);
240: }

242: /*MC
243:      KSPRICHARDSON - The preconditioned Richardson iterative method

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

248:    Level: beginner

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

252:           Here B is the application of the preconditioner

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

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

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

265:     Supports only left preconditioning

267:   References:
268:   "The Approximate Arithmetical Solution by Finite Differences of Physical Problems Involving
269:    Differential Equations, with an Application to the Stresses in a Masonry Dam",
270:   L. F. Richardson, Philosophical Transactions of the Royal Society of London. Series A,
271:   Containing Papers of a Mathematical or Physical Character, Vol. 210, 1911 (1911), pp. 307-357.

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

276: M*/

280: PETSC_EXTERN PetscErrorCode KSPCreate_Richardson(KSP ksp)
281: {
283:   KSP_Richardson *richardsonP;

286:   PetscNewLog(ksp,&richardsonP);
287:   ksp->data = (void*)richardsonP;

289:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,2);
290:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_LEFT,1);

292:   ksp->ops->setup          = KSPSetUp_Richardson;
293:   ksp->ops->solve          = KSPSolve_Richardson;
294:   ksp->ops->destroy        = KSPDestroy_Richardson;
295:   ksp->ops->buildsolution  = KSPBuildSolutionDefault;
296:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
297:   ksp->ops->view           = KSPView_Richardson;
298:   ksp->ops->setfromoptions = KSPSetFromOptions_Richardson;

300:   PetscObjectComposeFunction((PetscObject)ksp,"KSPRichardsonSetScale_C",KSPRichardsonSetScale_Richardson);
301:   PetscObjectComposeFunction((PetscObject)ksp,"KSPRichardsonSetSelfScale_C",KSPRichardsonSetSelfScale_Richardson);

303:   richardsonP->scale = 1.0;
304:   return(0);
305: }