Actual source code: fbcgs.c

petsc-3.8.2 2017-11-09
Report Typos and Errors

  2: /*
  3:     This file implements flexible BiCGStab (FBiCGStab).
  4:     Only allow right preconditioning.
  5: */
  6:  #include <../src/ksp/ksp/impls/bcgs/bcgsimpl.h>

  8: static PetscErrorCode KSPSetUp_FBCGS(KSP ksp)
  9: {

 13:   KSPSetWorkVecs(ksp,8);
 14:   return(0);
 15: }

 17: /* Only need a few hacks from KSPSolve_BCGS */

 19: static PetscErrorCode  KSPSolve_FBCGS(KSP ksp)
 20: {
 22:   PetscInt       i;
 23:   PetscScalar    rho,rhoold,alpha,beta,omega,omegaold,d1;
 24:   Vec            X,B,V,P,R,RP,T,S,P2,S2;
 25:   PetscReal      dp    = 0.0,d2;
 26:   KSP_BCGS       *bcgs = (KSP_BCGS*)ksp->data;
 27:   PC             pc;
 28:   Mat            mat;

 31:   X  = ksp->vec_sol;
 32:   B  = ksp->vec_rhs;
 33:   R  = ksp->work[0];
 34:   RP = ksp->work[1];
 35:   V  = ksp->work[2];
 36:   T  = ksp->work[3];
 37:   S  = ksp->work[4];
 38:   P  = ksp->work[5];
 39:   S2 = ksp->work[6];
 40:   P2 = ksp->work[7];

 42:   /* Only supports right preconditioning */
 43:   if (ksp->pc_side != PC_RIGHT) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"KSP fbcgs does not support %s",PCSides[ksp->pc_side]);
 44:   if (!ksp->guess_zero) {
 45:     if (!bcgs->guess) {
 46:       VecDuplicate(X,&bcgs->guess);
 47:     }
 48:     VecCopy(X,bcgs->guess);
 49:   } else {
 50:     VecSet(X,0.0);
 51:   }

 53:   /* Compute initial residual */
 54:   KSPGetPC(ksp,&pc);
 55:   PCSetUp(pc);
 56:   PCGetOperators(pc,&mat,NULL);
 57:   if (!ksp->guess_zero) {
 58:     KSP_MatMult(ksp,mat,X,S2);
 59:     VecCopy(B,R);
 60:     VecAXPY(R,-1.0,S2);
 61:   } else {
 62:     VecCopy(B,R);
 63:   }

 65:   /* Test for nothing to do */
 66:   if (ksp->normtype != KSP_NORM_NONE) {
 67:     VecNorm(R,NORM_2,&dp);
 68:   }
 69:   PetscObjectSAWsTakeAccess((PetscObject)ksp);
 70:   ksp->its   = 0;
 71:   ksp->rnorm = dp;
 72:   PetscObjectSAWsGrantAccess((PetscObject)ksp);
 73:   KSPLogResidualHistory(ksp,dp);
 74:   KSPMonitor(ksp,0,dp);
 75:   (*ksp->converged)(ksp,0,dp,&ksp->reason,ksp->cnvP);
 76:   if (ksp->reason) return(0);

 78:   /* Make the initial Rp == R */
 79:   VecCopy(R,RP);

 81:   rhoold   = 1.0;
 82:   alpha    = 1.0;
 83:   omegaold = 1.0;
 84:   VecSet(P,0.0);
 85:   VecSet(V,0.0);

 87:   i=0;
 88:   do {
 89:     VecDot(R,RP,&rho); /* rho <- (r,rp) */
 90:     beta = (rho/rhoold) * (alpha/omegaold);
 91:     VecAXPBYPCZ(P,1.0,-omegaold*beta,beta,R,V); /* p <- r - omega * beta* v + beta * p */

 93:     KSP_PCApply(ksp,P,P2); /* p2 <- K p */
 94:     KSP_MatMult(ksp,mat,P2,V); /* v <- A p2 */

 96:     VecDot(V,RP,&d1);
 97:     if (d1 == 0.0) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_PLIB,"Divide by zero");
 98:     alpha = rho / d1; /* alpha <- rho / (v,rp) */
 99:     VecWAXPY(S,-alpha,V,R); /* s <- r - alpha v */

101:     KSP_PCApply(ksp,S,S2); /* s2 <- K s */
102:     KSP_MatMult(ksp,mat,S2,T); /* t <- A s2 */

104:     VecDotNorm2(S,T,&d1,&d2);
105:     if (d2 == 0.0) {
106:       /* t is 0. if s is 0, then alpha v == r, and hence alpha p may be our solution. Give it a try? */
107:       VecDot(S,S,&d1);
108:       if (d1 != 0.0) {
109:         ksp->reason = KSP_DIVERGED_BREAKDOWN;
110:         break;
111:       }
112:       VecAXPY(X,alpha,P2);   /* x <- x + alpha p2 */
113:       PetscObjectSAWsTakeAccess((PetscObject)ksp);
114:       ksp->its++;
115:       ksp->rnorm  = 0.0;
116:       ksp->reason = KSP_CONVERGED_RTOL;
117:       PetscObjectSAWsGrantAccess((PetscObject)ksp);
118:       KSPLogResidualHistory(ksp,dp);
119:       KSPMonitor(ksp,i+1,0.0);
120:       break;
121:     }
122:     omega = d1 / d2; /* omega <- (t's) / (t't) */
123:     VecAXPBYPCZ(X,alpha,omega,1.0,P2,S2); /* x <- alpha * p2 + omega * s2 + x */

125:     VecWAXPY(R,-omega,T,S);  /* r <- s - omega t */
126:     if (ksp->normtype != KSP_NORM_NONE && ksp->chknorm < i+2) {
127:       VecNorm(R,NORM_2,&dp);
128:     }

130:     rhoold   = rho;
131:     omegaold = omega;

133:     PetscObjectSAWsTakeAccess((PetscObject)ksp);
134:     ksp->its++;
135:     ksp->rnorm = dp;
136:     PetscObjectSAWsGrantAccess((PetscObject)ksp);
137:     KSPLogResidualHistory(ksp,dp);
138:     KSPMonitor(ksp,i+1,dp);
139:     (*ksp->converged)(ksp,i+1,dp,&ksp->reason,ksp->cnvP);
140:     if (ksp->reason) break;
141:     if (rho == 0.0) {
142:       ksp->reason = KSP_DIVERGED_BREAKDOWN;
143:       break;
144:     }
145:     i++;
146:   } while (i<ksp->max_it);

148:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
149:   return(0);
150: }

152: /*MC
153:      KSPFBCGS - Implements flexible BiCGStab method.

155:    Options Database Keys:
156: .   see KSPSolve()

158:    Level: beginner

160:    Notes: Only allow right preconditioning

162: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPBICG, KSPFBCGSL, KSPSetPCSide()
163: M*/
164: PETSC_EXTERN PetscErrorCode KSPCreate_FBCGS(KSP ksp)
165: {
167:   KSP_BCGS       *bcgs;

170:   PetscNewLog(ksp,&bcgs);

172:   ksp->data                = bcgs;
173:   ksp->ops->setup          = KSPSetUp_FBCGS;
174:   ksp->ops->solve          = KSPSolve_FBCGS;
175:   ksp->ops->destroy        = KSPDestroy_BCGS;
176:   ksp->ops->reset          = KSPReset_BCGS;
177:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
178:   ksp->ops->setfromoptions = KSPSetFromOptions_BCGS;
179:   ksp->pc_side             = PC_RIGHT;  /* set default PC side */

181:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,3);
182:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,2);
183:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,1);
184:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_RIGHT,1);
185:   return(0);
186: }