Actual source code: pcksp.c

petsc-master 2019-09-20
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  1:  #include <petsc/private/pcimpl.h>
  2:  #include <petsc/private/kspimpl.h>
  3:  #include <petscksp.h>

  5: typedef struct {
  6:   KSP      ksp;
  7:   PetscInt its; /* total number of iterations KSP uses */
  8: } PC_KSP;

 10: static PetscErrorCode  PCKSPCreateKSP_KSP(PC pc)
 11: {
 13:   const char     *prefix;
 14:   PC_KSP         *jac = (PC_KSP*)pc->data;
 15:   DM             dm;

 18:   KSPCreate(PetscObjectComm((PetscObject)pc),&jac->ksp);
 19:   KSPSetErrorIfNotConverged(jac->ksp,pc->erroriffailure);
 20:   PetscObjectIncrementTabLevel((PetscObject)jac->ksp,(PetscObject)pc,1);
 21:   PCGetOptionsPrefix(pc,&prefix);
 22:   KSPSetOptionsPrefix(jac->ksp,prefix);
 23:   KSPAppendOptionsPrefix(jac->ksp,"ksp_");
 24:   PCGetDM(pc, &dm);
 25:   if (dm) {
 26:     KSPSetDM(jac->ksp, dm);
 27:     KSPSetDMActive(jac->ksp, PETSC_FALSE);
 28:   }
 29:   return(0);
 30: }

 32: static PetscErrorCode PCApply_KSP(PC pc,Vec x,Vec y)
 33: {
 34:   PetscErrorCode     ierr;
 35:   PetscInt           its;
 36:   PC_KSP             *jac = (PC_KSP*)pc->data;

 39:   if (jac->ksp->presolve) {
 40:     VecCopy(x,y);
 41:     KSPSolve(jac->ksp,y,y);
 42:   } else {
 43:     KSPSolve(jac->ksp,x,y);
 44:   }
 45:   KSPCheckSolve(jac->ksp,pc,y);
 46:   KSPGetIterationNumber(jac->ksp,&its);
 47:   jac->its += its;
 48:   return(0);
 49: }

 51: static PetscErrorCode PCApplyTranspose_KSP(PC pc,Vec x,Vec y)
 52: {
 53:   PetscErrorCode     ierr;
 54:   PetscInt           its;
 55:   PC_KSP             *jac = (PC_KSP*)pc->data;

 58:   if (jac->ksp->presolve) {
 59:     VecCopy(x,y);
 60:     KSPSolve(jac->ksp,y,y);
 61:   } else {
 62:     KSPSolveTranspose(jac->ksp,x,y);
 63:   }
 64:   KSPCheckSolve(jac->ksp,pc,y);
 65:   KSPGetIterationNumber(jac->ksp,&its);
 66:   jac->its += its;
 67:   return(0);
 68: }

 70: static PetscErrorCode PCSetUp_KSP(PC pc)
 71: {
 73:   PC_KSP         *jac = (PC_KSP*)pc->data;
 74:   Mat            mat;

 77:   if (!jac->ksp) {
 78:     PCKSPCreateKSP_KSP(pc);
 79:     KSPSetFromOptions(jac->ksp);
 80:   }
 81:   if (pc->useAmat) mat = pc->mat;
 82:   else             mat = pc->pmat;
 83:   KSPSetOperators(jac->ksp,mat,pc->pmat);
 84:   KSPSetUp(jac->ksp);
 85:   return(0);
 86: }

 88: /* Default destroy, if it has never been setup */
 89: static PetscErrorCode PCReset_KSP(PC pc)
 90: {
 91:   PC_KSP         *jac = (PC_KSP*)pc->data;

 95:   KSPDestroy(&jac->ksp);
 96:   return(0);
 97: }

 99: static PetscErrorCode PCDestroy_KSP(PC pc)
100: {
101:   PC_KSP         *jac = (PC_KSP*)pc->data;

105:   KSPDestroy(&jac->ksp);
106:   PetscObjectComposeFunction((PetscObject)pc,"PCKSPGetKSP_C",NULL);
107:   PetscObjectComposeFunction((PetscObject)pc,"PCKSPSetKSP_C",NULL);
108:   PetscFree(pc->data);
109:   return(0);
110: }

112: static PetscErrorCode PCView_KSP(PC pc,PetscViewer viewer)
113: {
114:   PC_KSP         *jac = (PC_KSP*)pc->data;
116:   PetscBool      iascii;

119:   if (!jac->ksp) {PCKSPCreateKSP_KSP(pc);}
120:   PetscObjectTypeCompare((PetscObject)viewer,PETSCVIEWERASCII,&iascii);
121:   if (iascii) {
122:     if (pc->useAmat) {
123:       PetscViewerASCIIPrintf(viewer,"  Using Amat (not Pmat) as operator on inner solve\n");
124:     }
125:     PetscViewerASCIIPrintf(viewer,"  KSP and PC on KSP preconditioner follow\n");
126:     PetscViewerASCIIPrintf(viewer,"  ---------------------------------\n");
127:   }
128:   PetscViewerASCIIPushTab(viewer);
129:   KSPView(jac->ksp,viewer);
130:   PetscViewerASCIIPopTab(viewer);
131:   if (iascii) {
132:     PetscViewerASCIIPrintf(viewer,"  ---------------------------------\n");
133:   }
134:   return(0);
135: }

137: static PetscErrorCode  PCKSPSetKSP_KSP(PC pc,KSP ksp)
138: {
139:   PC_KSP         *jac = (PC_KSP*)pc->data;

143:   PetscObjectReference((PetscObject)ksp);
144:   KSPDestroy(&jac->ksp);
145:   jac->ksp = ksp;
146:   return(0);
147: }

149: /*@
150:    PCKSPSetKSP - Sets the KSP context for a KSP PC.

152:    Collective on PC

154:    Input Parameter:
155: +  pc - the preconditioner context
156: -  ksp - the KSP solver

158:    Notes:
159:    The PC and the KSP must have the same communicator

161:    Level: advanced

163: @*/
164: PetscErrorCode  PCKSPSetKSP(PC pc,KSP ksp)
165: {

172:   PetscTryMethod(pc,"PCKSPSetKSP_C",(PC,KSP),(pc,ksp));
173:   return(0);
174: }

176: static PetscErrorCode  PCKSPGetKSP_KSP(PC pc,KSP *ksp)
177: {
178:   PC_KSP         *jac = (PC_KSP*)pc->data;

182:   if (!jac->ksp) {PCKSPCreateKSP_KSP(pc);}
183:   *ksp = jac->ksp;
184:   return(0);
185: }

187: /*@
188:    PCKSPGetKSP - Gets the KSP context for a KSP PC.

190:    Not Collective but KSP returned is parallel if PC was parallel

192:    Input Parameter:
193: .  pc - the preconditioner context

195:    Output Parameters:
196: .  ksp - the KSP solver

198:    Notes:
199:    You must call KSPSetUp() before calling PCKSPGetKSP().

201:    If the PC is not a PCKSP object it raises an error

203:    Level: advanced

205: @*/
206: PetscErrorCode  PCKSPGetKSP(PC pc,KSP *ksp)
207: {

213:   PetscUseMethod(pc,"PCKSPGetKSP_C",(PC,KSP*),(pc,ksp));
214:   return(0);
215: }

217: static PetscErrorCode PCSetFromOptions_KSP(PetscOptionItems *PetscOptionsObject,PC pc)
218: {
219:   PC_KSP         *jac = (PC_KSP*)pc->data;

223:   PetscOptionsHead(PetscOptionsObject,"PC KSP options");
224:   if (jac->ksp) {
225:     KSPSetFromOptions(jac->ksp);
226:    }
227:   PetscOptionsTail();
228:   return(0);
229: }

231: /* ----------------------------------------------------------------------------------*/

233: /*MC
234:      PCKSP -    Defines a preconditioner that can consist of any KSP solver.
235:                  This allows, for example, embedding a Krylov method inside a preconditioner.

237:    Options Database Key:
238: .     -pc_use_amat - use the matrix that defines the linear system, Amat as the matrix for the
239:                     inner solver, otherwise by default it uses the matrix used to construct
240:                     the preconditioner, Pmat (see PCSetOperators())

242:    Level: intermediate

244:    Notes:
245:     Using a Krylov method inside another Krylov method can be dangerous (you get divergence or
246:           the incorrect answer) unless you use KSPFGMRES as the other Krylov method

248:    Developer Notes:
249:     If the outer Krylov method has a nonzero initial guess it will compute a new residual based on that initial guess
250:     and pass that as the right hand side into this KSP (and hence this KSP will always have a zero initial guess). For all outer Krylov methods
251:     except Richardson this is neccessary since Krylov methods, even the flexible ones, need to "see" the result of the action of the preconditioner on the
252:     input (current residual) vector, the action of the preconditioner cannot depend also on some other vector (the "initial guess"). For
253:     KSPRICHARDSON it is possible to provide a PCApplyRichardson_PCKSP() that short circuits returning to the KSP object at each iteration to compute the
254:     residual, see for example PCApplyRichardson_SOR(). We do not implement a PCApplyRichardson_PCKSP()  because (1) using a KSP directly inside a Richardson
255:     is not an efficient algorithm anyways and (2) implementing it for its > 1 would essentially require that we implement Richardson (reimplementing the
256:     Richardson code) inside the PCApplyRichardson_PCKSP() leading to duplicate code.

258: .seealso:  PCCreate(), PCSetType(), PCType (for list of available types), PC,
259:            PCSHELL, PCCOMPOSITE, PCSetUseAmat(), PCKSPGetKSP()

261: M*/

263: PETSC_EXTERN PetscErrorCode PCCreate_KSP(PC pc)
264: {
266:   PC_KSP         *jac;

269:   PetscNewLog(pc,&jac);
270:   pc->data = (void*)jac;

272:   PetscMemzero(pc->ops,sizeof(struct _PCOps));
273:   pc->ops->apply           = PCApply_KSP;
274:   pc->ops->applytranspose  = PCApplyTranspose_KSP;
275:   pc->ops->setup           = PCSetUp_KSP;
276:   pc->ops->reset           = PCReset_KSP;
277:   pc->ops->destroy         = PCDestroy_KSP;
278:   pc->ops->setfromoptions  = PCSetFromOptions_KSP;
279:   pc->ops->view            = PCView_KSP;

281:   PetscObjectComposeFunction((PetscObject)pc,"PCKSPGetKSP_C",PCKSPGetKSP_KSP);
282:   PetscObjectComposeFunction((PetscObject)pc,"PCKSPSetKSP_C",PCKSPSetKSP_KSP);
283:   return(0);
284: }