Date: 2022-08-02T03:14:38+00:00

Actual source code: bcgs.c

      2: #include <../src/ksp/ksp/impls/bcgs/bcgsimpl.h>

      4: PetscErrorCode KSPSetFromOptions_BCGS(PetscOptionItems *PetscOptionsObject,KSP ksp)
      5: {
      6:   PetscOptionsHead(PetscOptionsObject,"KSP BCGS Options");
      7:   PetscOptionsTail();
      8:   return 0;
      9: }

     11: PetscErrorCode KSPSetUp_BCGS(KSP ksp)
     12: {
     13:   KSPSetWorkVecs(ksp,6);
     14:   return 0;
     15: }

     17: PetscErrorCode KSPSolve_BCGS(KSP ksp)
     18: {
     19:   PetscInt       i;
     20:   PetscScalar    rho,rhoold,alpha,beta,omega,omegaold,d1;
     21:   Vec            X,B,V,P,R,RP,T,S;
     22:   PetscReal      dp    = 0.0,d2;
     23:   KSP_BCGS       *bcgs = (KSP_BCGS*)ksp->data;

     25:   X  = ksp->vec_sol;
     26:   B  = ksp->vec_rhs;
     27:   R  = ksp->work[0];
     28:   RP = ksp->work[1];
     29:   V  = ksp->work[2];
     30:   T  = ksp->work[3];
     31:   S  = ksp->work[4];
     32:   P  = ksp->work[5];

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

     37:   /* with right preconditioning need to save initial guess to add to final solution */
     38:   if (ksp->pc_side == PC_RIGHT && !ksp->guess_zero) {
     39:     if (!bcgs->guess) {
     40:       VecDuplicate(X,&bcgs->guess);
     41:     }
     42:     VecCopy(X,bcgs->guess);
     43:     VecSet(X,0.0);
     44:   }

     46:   /* Test for nothing to do */
     47:   if (ksp->normtype != KSP_NORM_NONE) {
     48:     VecNorm(R,NORM_2,&dp);
     49:     KSPCheckNorm(ksp,dp);
     50:   }
     51:   PetscObjectSAWsTakeAccess((PetscObject)ksp);
     52:   ksp->its   = 0;
     53:   ksp->rnorm = dp;
     54:   PetscObjectSAWsGrantAccess((PetscObject)ksp);
     55:   KSPLogResidualHistory(ksp,dp);
     56:   KSPMonitor(ksp,0,dp);
     57:   (*ksp->converged)(ksp,0,dp,&ksp->reason,ksp->cnvP);
     58:   if (ksp->reason) {
     59:     if (bcgs->guess) {
     60:       VecAXPY(X,1.0,bcgs->guess);
     61:     }
     62:     return 0;
     63:   }

     65:   /* Make the initial Rp == R */
     66:   VecCopy(R,RP);

     68:   rhoold   = 1.0;
     69:   alpha    = 1.0;
     70:   omegaold = 1.0;
     71:   VecSet(P,0.0);
     72:   VecSet(V,0.0);

     74:   i = 0;
     75:   do {
     76:     VecDot(R,RP,&rho);       /*   rho <- (r,rp)      */
     77:     beta = (rho/rhoold) * (alpha/omegaold);
     78:     VecAXPBYPCZ(P,1.0,-omegaold*beta,beta,R,V);  /* p <- r - omega * beta* v + beta * p */
     79:     KSP_PCApplyBAorAB(ksp,P,V,T);  /*   v <- K p           */
     80:     VecDot(V,RP,&d1);
     81:     KSPCheckDot(ksp,d1);
     82:     if (d1 == 0.0) {
     84:       else ksp->reason = KSP_DIVERGED_BREAKDOWN;
     85:       PetscInfo(ksp,"Breakdown due to zero inner product\n");
     86:       break;
     87:     }
     88:     alpha = rho / d1;                 /*   a <- rho / (v,rp)  */
     89:     VecWAXPY(S,-alpha,V,R);     /*   s <- r - a v       */
     90:     KSP_PCApplyBAorAB(ksp,S,T,R); /*   t <- K s    */
     91:     VecDotNorm2(S,T,&d1,&d2);
     92:     if (d2 == 0.0) {
     93:       /* t is 0.  if s is 0, then alpha v == r, and hence alpha p
     94:          may be our solution.  Give it a try? */
     95:       VecDot(S,S,&d1);
     96:       if (d1 != 0.0) {
     98:         else ksp->reason = KSP_DIVERGED_BREAKDOWN;
     99:         PetscInfo(ksp,"Failed due to singular preconditioned operator\n");
    100:         break;
    101:       }
    102:       VecAXPY(X,alpha,P);   /*   x <- x + a p       */
    103:       PetscObjectSAWsTakeAccess((PetscObject)ksp);
    104:       ksp->its++;
    105:       ksp->rnorm  = 0.0;
    106:       ksp->reason = KSP_CONVERGED_RTOL;
    107:       PetscObjectSAWsGrantAccess((PetscObject)ksp);
    108:       KSPLogResidualHistory(ksp,dp);
    109:       KSPMonitor(ksp,i+1,0.0);
    110:       break;
    111:     }
    112:     omega = d1 / d2;                               /*   w <- (t's) / (t't) */
    113:     VecAXPBYPCZ(X,alpha,omega,1.0,P,S); /* x <- alpha * p + omega * s + x */
    114:     VecWAXPY(R,-omega,T,S);     /*   r <- s - w t       */
    115:     if (ksp->normtype != KSP_NORM_NONE && ksp->chknorm < i+2) {
    116:       VecNorm(R,NORM_2,&dp);
    117:       KSPCheckNorm(ksp,dp);
    118:     }

    120:     rhoold   = rho;
    121:     omegaold = omega;

    123:     PetscObjectSAWsTakeAccess((PetscObject)ksp);
    124:     ksp->its++;
    125:     ksp->rnorm = dp;
    126:     PetscObjectSAWsGrantAccess((PetscObject)ksp);
    127:     KSPLogResidualHistory(ksp,dp);
    128:     KSPMonitor(ksp,i+1,dp);
    129:     (*ksp->converged)(ksp,i+1,dp,&ksp->reason,ksp->cnvP);
    130:     if (ksp->reason) break;
    131:     if (rho == 0.0) {
    133:       else ksp->reason = KSP_DIVERGED_BREAKDOWN;
    134:       PetscInfo(ksp,"Breakdown due to zero rho inner product\n");
    135:       break;
    136:     }
    137:     i++;
    138:   } while (i<ksp->max_it);

    140:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;

    142:   KSPUnwindPreconditioner(ksp,X,T);
    143:   if (bcgs->guess) {
    144:     VecAXPY(X,1.0,bcgs->guess);
    145:   }
    146:   return 0;
    147: }

    149: PetscErrorCode KSPBuildSolution_BCGS(KSP ksp,Vec v,Vec *V)
    150: {
    151:   KSP_BCGS       *bcgs = (KSP_BCGS*)ksp->data;

    153:   if (ksp->pc_side == PC_RIGHT) {
    154:     if (v) {
    155:       KSP_PCApply(ksp,ksp->vec_sol,v);
    156:       if (bcgs->guess) {
    157:         VecAXPY(v,1.0,bcgs->guess);
    158:       }
    159:       *V = v;
    160:     } else SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"Not working with right preconditioner");
    161:   } else {
    162:     if (v) {
    163:       VecCopy(ksp->vec_sol,v); *V = v;
    164:     } else *V = ksp->vec_sol;
    165:   }
    166:   return 0;
    167: }

    169: PetscErrorCode KSPReset_BCGS(KSP ksp)
    170: {
    171:   KSP_BCGS       *cg = (KSP_BCGS*)ksp->data;

    173:   VecDestroy(&cg->guess);
    174:   return 0;
    175: }

    177: PetscErrorCode KSPDestroy_BCGS(KSP ksp)
    178: {
    179:   KSPReset_BCGS(ksp);
    180:   KSPDestroyDefault(ksp);
    181:   return 0;
    182: }

    184: /*MC
    185:      KSPBCGS - Implements the BiCGStab (Stabilized version of BiConjugate Gradient) method.

    187:    Options Database Keys:
    188:     see KSPSolve()

    190:    Level: beginner

    192:    Notes:
    193:     See KSPBCGSL for additional stabilization
    194:           Supports left and right preconditioning but not symmetric

    196:    References:
    197: .  * - van der Vorst, SIAM J. Sci. Stat. Comput., 1992.

    199: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPBICG, KSPBCGSL, KSPFBICG, KSPQMRCGS, KSPSetPCSide()
    200: M*/
    201: PETSC_EXTERN PetscErrorCode KSPCreate_BCGS(KSP ksp)
    202: {
    203:   KSP_BCGS       *bcgs;

    205:   PetscNewLog(ksp,&bcgs);

    207:   ksp->data                = bcgs;
    208:   ksp->ops->setup          = KSPSetUp_BCGS;
    209:   ksp->ops->solve          = KSPSolve_BCGS;
    210:   ksp->ops->destroy        = KSPDestroy_BCGS;
    211:   ksp->ops->reset          = KSPReset_BCGS;
    212:   ksp->ops->buildsolution  = KSPBuildSolution_BCGS;
    213:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
    214:   ksp->ops->setfromoptions = KSPSetFromOptions_BCGS;

    216:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,3);
    217:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,2);
    218:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,1);
    219:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_RIGHT,1);
    220:   return 0;
    221: }