Actual source code: bcgs.c

  1: #define PETSCKSP_DLL

 3:  #include private/kspimpl.h

  7: static PetscErrorCode KSPSetUp_BCGS(KSP ksp)
  8: {

 12:   if (ksp->pc_side == PC_SYMMETRIC) {
 13:     SETERRQ(PETSC_ERR_SUP,"no symmetric preconditioning for KSPBCGS");
 14:   }
 15:   KSPDefaultGetWork(ksp,6);
 16:   return(0);
 17: }

 21: static PetscErrorCode  KSPSolve_BCGS(KSP ksp)
 22: {
 24:   PetscInt       i;
 25:   PetscScalar    rho,rhoold,alpha,beta,omega,omegaold,d1,d2;
 26:   Vec            X,B,V,P,R,RP,T,S;
 27:   PetscReal      dp = 0.0;

 30:   if (ksp->normtype == KSP_NORM_NATURAL) SETERRQ(PETSC_ERR_SUP,"Cannot use natural residual norm with KSPBCGS");
 31:   if (ksp->normtype == KSP_NORM_PRECONDITIONED && ksp->pc_side != PC_LEFT) SETERRQ(PETSC_ERR_SUP,"Use -ksp_norm_type unpreconditioned for right preconditioning and KSPBCGS");
 32:   if (ksp->normtype == KSP_NORM_UNPRECONDITIONED && ksp->pc_side != PC_RIGHT) SETERRQ(PETSC_ERR_SUP,"Use -ksp_norm_type preconditioned for left preconditioning and KSPBCGS");

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

 43:   /* Compute initial preconditioned residual */
 44:   KSPInitialResidual(ksp,X,V,T,R,B);

 46:   /* Test for nothing to do */
 47:   if (ksp->normtype != KSP_NORM_NO) {
 48:     VecNorm(R,NORM_2,&dp);
 49:   }
 50:   PetscObjectTakeAccess(ksp);
 51:   ksp->its   = 0;
 52:   ksp->rnorm = dp;
 53:   PetscObjectGrantAccess(ksp);
 54:   KSPLogResidualHistory(ksp,dp);
 55:   KSPMonitor(ksp,0,dp);
 56:   (*ksp->converged)(ksp,0,dp,&ksp->reason,ksp->cnvP);
 57:   if (ksp->reason) return(0);

 59:   /* Make the initial Rp == R */
 60:   VecCopy(R,RP);

 62:   rhoold   = 1.0;
 63:   alpha    = 1.0;
 64:   omegaold = 1.0;
 65:   VecSet(P,0.0);
 66:   VecSet(V,0.0);

 68:   i=0;
 69:   do {
 70:     VecDot(R,RP,&rho);       /*   rho <- (r,rp)      */
 71:     beta = (rho/rhoold) * (alpha/omegaold);
 72:     VecAXPBYPCZ(P,1.0,-omegaold*beta,beta,R,V);  /* p <- r - omega * beta* v + beta * p */
 73:     KSP_PCApplyBAorAB(ksp,P,V,T);  /*   v <- K p           */
 74:     VecDot(V,RP,&d1);
 75:     if (d1 == 0.0) SETERRQ(PETSC_ERR_PLIB,"Divide by zero");
 76:     alpha = rho / d1;                 /*   a <- rho / (v,rp)  */
 77:     VecWAXPY(S,-alpha,V,R);      /*   s <- r - a v       */
 78:     KSP_PCApplyBAorAB(ksp,S,T,R);/*   t <- K s    */
 79:     VecDotNorm2(S,T,&d1,&d2);
 80:     if (d2 == 0.0) {
 81:       /* t is 0.  if s is 0, then alpha v == r, and hence alpha p
 82:          may be our solution.  Give it a try? */
 83:       VecDot(S,S,&d1);
 84:       if (d1 != 0.0) {
 85:         ksp->reason = KSP_DIVERGED_BREAKDOWN;
 86:         break;
 87:       }
 88:       VecAXPY(X,alpha,P);   /*   x <- x + a p       */
 89:       PetscObjectTakeAccess(ksp);
 90:       ksp->its++;
 91:       ksp->rnorm  = 0.0;
 92:       ksp->reason = KSP_CONVERGED_RTOL;
 93:       PetscObjectGrantAccess(ksp);
 94:       KSPLogResidualHistory(ksp,dp);
 95:       KSPMonitor(ksp,i+1,0.0);
 96:       break;
 97:     }
 98:     omega = d1 / d2;                               /*   w <- (t's) / (t't) */
 99:     VecAXPBYPCZ(X,alpha,omega,1.0,P,S); /* x <- alpha * p + omega * s + x */
100:     VecWAXPY(R,-omega,T,S);     /*   r <- s - w t       */
101:     if (ksp->normtype != KSP_NORM_NO && ksp->chknorm < i+2) {
102:       VecNorm(R,NORM_2,&dp);
103:     }

105:     rhoold   = rho;
106:     omegaold = omega;

108:     PetscObjectTakeAccess(ksp);
109:     ksp->its++;
110:     ksp->rnorm = dp;
111:     PetscObjectGrantAccess(ksp);
112:     KSPLogResidualHistory(ksp,dp);
113:     KSPMonitor(ksp,i+1,dp);
114:     (*ksp->converged)(ksp,i+1,dp,&ksp->reason,ksp->cnvP);
115:     if (ksp->reason) break;
116:     if (rho == 0.0) {
117:       ksp->reason = KSP_DIVERGED_BREAKDOWN;
118:       break;
119:     }
120:     i++;
121:   } while (i<ksp->max_it);

123:   if (i >= ksp->max_it) {
124:     ksp->reason = KSP_DIVERGED_ITS;
125:   }

127:   KSPUnwindPreconditioner(ksp,X,T);
128:   return(0);
129: }

131: /*MC
132:      KSPBCGS - Implements the BiCGStab (Stabilized version of BiConjugate Gradient Squared) method.

134:    Options Database Keys:
135: .   see KSPSolve()

137:    Level: beginner

139:    Notes: Reference: van der Vorst, SIAM J. Sci. Stat. Comput., 1992.
140:           See KSPBCGSL for additional stabilization


143: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPBICG, KSPBCGSL
144: M*/
148: PetscErrorCode  KSPCreate_BCGS(KSP ksp)
149: {
151:   ksp->data                 = (void*)0;
152:   ksp->pc_side              = PC_LEFT;
153:   ksp->ops->setup           = KSPSetUp_BCGS;
154:   ksp->ops->solve           = KSPSolve_BCGS;
155:   ksp->ops->destroy         = KSPDefaultDestroy;
156:   ksp->ops->buildsolution   = KSPDefaultBuildSolution;
157:   ksp->ops->buildresidual   = KSPDefaultBuildResidual;
158:   ksp->ops->setfromoptions  = 0;
159:   ksp->ops->view            = 0;
160:   return(0);
161: }