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

 10: static PetscErrorCode KSPSetUp_FBCGS(KSP ksp)
 11: {

 15:   KSPSetWorkVecs(ksp,8);
 16:   return(0);
 17: }

 19: /* Only need a few hacks from KSPSolve_BCGS */
 20: #include <petsc-private/pcimpl.h>            /*I "petscksp.h" I*/
 23: static PetscErrorCode  KSPSolve_FBCGS(KSP ksp)
 24: {
 26:   PetscInt       i;
 27:   PetscScalar    rho,rhoold,alpha,beta,omega,omegaold,d1;
 28:   Vec            X,B,V,P,R,RP,T,S,P2,S2;
 29:   PetscReal      dp    = 0.0,d2;
 30:   KSP_BCGS       *bcgs = (KSP_BCGS*)ksp->data;
 31:   PC             pc;

 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];
 42:   S2 = ksp->work[6];
 43:   P2 = ksp->work[7];

 45:   /* Only supports right preconditioning */
 46:   if (ksp->pc_side != PC_RIGHT) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"KSP fbcgs does not support %s",PCSides[ksp->pc_side]);
 47:   if (!ksp->guess_zero) {
 48:     if (!bcgs->guess) {
 49:       VecDuplicate(X,&bcgs->guess);
 50:     }
 51:     VecCopy(X,bcgs->guess);
 52:   } else {
 53:     VecSet(X,0.0);
 54:   }

 56:   /* Compute initial residual */
 57:   KSPGetPC(ksp,&pc);
 58:   PCSetUp(pc);
 59:   if (!ksp->guess_zero) {
 60:     MatMult(pc->mat,X,S2);
 61:     VecCopy(B,R);
 62:     VecAXPY(R,-1.0,S2);
 63:   } else {
 64:     VecCopy(B,R);
 65:   }

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

 80:   /* Make the initial Rp == R */
 81:   VecCopy(R,RP);

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

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

 95:     PCApply(pc,P,P2); /* p2 <- K p */
 96:     MatMult(pc->mat,P2,V); /* v <- A p2 */

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

103:     PCApply(pc,S,S2); /* s2 <- K s */
104:     MatMult(pc->mat,S2,T); /* t <- A s2 */

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

127:     VecWAXPY(R,-omega,T,S);  /* r <- s - omega t */
128:     if (ksp->normtype != KSP_NORM_NONE && ksp->chknorm < i+2) {
129:       VecNorm(R,NORM_2,&dp);
130:     }

132:     rhoold   = rho;
133:     omegaold = omega;

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

150:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
151:   return(0);
152: }

154: /*MC
155:      KSPFBCGS - Implements flexible BiCGStab method.

157:    Options Database Keys:
158: .   see KSPSolve()

160:    Level: beginner

162:    Notes: Only allow right preconditioning

164: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPBICG, KSPFBCGSL, KSPSetPCSide()
165: M*/
168: PETSC_EXTERN PetscErrorCode KSPCreate_FBCGS(KSP ksp)
169: {
171:   KSP_BCGS       *bcgs;

174:   PetscNewLog(ksp,&bcgs);

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

185:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,3);
186:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,2);
187:   return(0);
188: }