Date: 2015-10-02T22:20:49+00:00

Actual source code: fbcgsr.c
petsc-3.6.2 2015-10-02
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      2: /*
      3:     This file implements FBiCGStab-R.
      4:     Only allow right preconditioning.
      5:     FBiCGStab-R is a mathematically equivalent variant of FBiCGStab. Differences are:
      6:       (1) There are fewer MPI_Allreduce calls.
      7:       (2) The convergence occasionally is much faster than that of FBiCGStab.
      8: */
      9: #include <../src/ksp/ksp/impls/bcgs/bcgsimpl.h>       /*I  "petscksp.h"  I*/
     10: #include <petsc/private/vecimpl.h>

     14: PetscErrorCode KSPSetUp_FBCGSR(KSP ksp)
     15: {

     19:   KSPSetWorkVecs(ksp,8);
     20:   return(0);
     21: }

     23: #include <petsc/private/pcimpl.h>            /*I "petscksp.h" I*/
     26: PetscErrorCode  KSPSolve_FBCGSR(KSP ksp)
     27: {
     28:   PetscErrorCode    ierr;
     29:   PetscInt          i,j,N;
     30:   PetscScalar       tau,sigma,alpha,omega,beta;
     31:   PetscReal         rho;
     32:   PetscScalar       xi1,xi2,xi3,xi4;
     33:   Vec               X,B,P,P2,RP,R,V,S,T,S2;
     34:   PetscScalar       *PETSC_RESTRICT rp, *PETSC_RESTRICT r, *PETSC_RESTRICT p;
     35:   PetscScalar       *PETSC_RESTRICT v, *PETSC_RESTRICT s, *PETSC_RESTRICT t, *PETSC_RESTRICT s2;
     36:   PetscScalar       insums[4],outsums[4];
     37:   KSP_BCGS          *bcgs = (KSP_BCGS*)ksp->data;
     38:   PC                pc;

     41:   if (!ksp->vec_rhs->petscnative) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"Only coded for PETSc vectors");
     42:   VecGetLocalSize(ksp->vec_sol,&N);

     44:   X  = ksp->vec_sol;
     45:   B  = ksp->vec_rhs;
     46:   P2 = ksp->work[0];

     48:   /* The followings are involved in modified inner product calculations and vector updates */
     49:   RP = ksp->work[1]; VecGetArray(RP,(PetscScalar**)&rp); VecRestoreArray(RP,NULL);
     50:   R  = ksp->work[2]; VecGetArray(R,(PetscScalar**)&r);   VecRestoreArray(R,NULL);
     51:   P  = ksp->work[3]; VecGetArray(P,(PetscScalar**)&p);   VecRestoreArray(P,NULL);
     52:   V  = ksp->work[4]; VecGetArray(V,(PetscScalar**)&v);   VecRestoreArray(V,NULL);
     53:   S  = ksp->work[5]; VecGetArray(S,(PetscScalar**)&s);   VecRestoreArray(S,NULL);
     54:   T  = ksp->work[6]; VecGetArray(T,(PetscScalar**)&t);   VecRestoreArray(T,NULL);
     55:   S2 = ksp->work[7]; VecGetArray(S2,(PetscScalar**)&s2); VecRestoreArray(S2,NULL);

     57:   /* Only supports right preconditioning */
     58:   if (ksp->pc_side != PC_RIGHT) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"KSP fbcgsr does not support %s",PCSides[ksp->pc_side]);
     59:   if (!ksp->guess_zero) {
     60:     if (!bcgs->guess) {
     61:       VecDuplicate(X,&bcgs->guess);
     62:     }
     63:     VecCopy(X,bcgs->guess);
     64:   } else {
     65:     VecSet(X,0.0);
     66:   }

     68:   /* Compute initial residual */
     69:   KSPGetPC(ksp,&pc);
     70:   PCSetUp(pc);
     71:   if (!ksp->guess_zero) {
     72:     KSP_MatMult(ksp,pc->mat,X,P2); /* P2 is used as temporary storage */
     73:     VecCopy(B,R);
     74:     VecAXPY(R,-1.0,P2);
     75:   } else {
     76:     VecCopy(B,R);
     77:   }

     79:   /* Test for nothing to do */
     80:   if (ksp->normtype != KSP_NORM_NONE) {
     81:     VecNorm(R,NORM_2,&rho);
     82:   }
     83:   PetscObjectSAWsTakeAccess((PetscObject)ksp);
     84:   ksp->its   = 0;
     85:   ksp->rnorm = rho;
     86:   PetscObjectSAWsGrantAccess((PetscObject)ksp);
     87:   KSPLogResidualHistory(ksp,rho);
     88:   KSPMonitor(ksp,0,rho);
     89:   (*ksp->converged)(ksp,0,rho,&ksp->reason,ksp->cnvP);
     90:   if (ksp->reason) return(0);

     92:   /* Initialize iterates */
     93:   VecCopy(R,RP); /* rp <- r */
     94:   VecCopy(R,P); /* p <- r */

     96:   /* Big loop */
     97:   for (i=0; i<ksp->max_it; i++) {

     99:     /* matmult and pc */
    100:     KSP_PCApply(ksp,P,P2); /* p2 <- K p */
    101:     KSP_MatMult(ksp,pc->mat,P2,V); /* v <- A p2 */

    103:     /* inner prodcuts */
    104:     if (i==0) {
    105:       tau  = rho*rho;
    106:       VecDot(V,RP,&sigma); /* sigma <- (v,rp) */
    107:     } else {
    108:       PetscLogEventBegin(VEC_ReduceArithmetic,0,0,0,0);
    109:       tau  = sigma = 0.0;
    110:       for (j=0; j<N; j++) {
    111:         tau   += r[j]*rp[j]; /* tau <- (r,rp) */
    112:         sigma += v[j]*rp[j]; /* sigma <- (v,rp) */
    113:       }
    114:       PetscLogFlops(4.0*N);
    115:       PetscLogEventEnd(VEC_ReduceArithmetic,0,0,0,0);
    116:       insums[0] = tau;
    117:       insums[1] = sigma;
    118:       PetscLogEventBarrierBegin(VEC_ReduceBarrier,0,0,0,0,PetscObjectComm((PetscObject)ksp));
    119:       MPI_Allreduce(insums,outsums,2,MPIU_SCALAR,MPIU_SUM,PetscObjectComm((PetscObject)ksp));
    120:       PetscLogEventBarrierEnd(VEC_ReduceBarrier,0,0,0,0,PetscObjectComm((PetscObject)ksp));
    121:       tau       = outsums[0];
    122:       sigma     = outsums[1];
    123:     }

    125:     /* scalar update */
    126:     alpha = tau / sigma;

    128:     /* vector update */
    129:     VecWAXPY(S,-alpha,V,R);  /* s <- r - alpha v */

    131:     /* matmult and pc */
    132:     KSP_PCApply(ksp,S,S2); /* s2 <- K s */
    133:     KSP_MatMult(ksp,pc->mat,S2,T); /* t <- A s2 */

    135:     /* inner prodcuts */
    136:     PetscLogEventBegin(VEC_ReduceArithmetic,0,0,0,0);
    137:     xi1  = xi2 = xi3 = xi4 = 0.0;
    138:     for (j=0; j<N; j++) {
    139:       xi1 += s[j]*s[j]; /* xi1 <- (s,s) */
    140:       xi2 += t[j]*s[j]; /* xi2 <- (t,s) */
    141:       xi3 += t[j]*t[j]; /* xi3 <- (t,t) */
    142:       xi4 += t[j]*rp[j]; /* xi4 <- (t,rp) */
    143:     }
    144:     PetscLogFlops(8.0*N);
    145:     PetscLogEventEnd(VEC_ReduceArithmetic,0,0,0,0);

    147:     insums[0] = xi1;
    148:     insums[1] = xi2;
    149:     insums[2] = xi3;
    150:     insums[3] = xi4;

    152:     PetscLogEventBarrierBegin(VEC_ReduceBarrier,0,0,0,0,PetscObjectComm((PetscObject)ksp));
    153:     MPI_Allreduce(insums,outsums,4,MPIU_SCALAR,MPIU_SUM,PetscObjectComm((PetscObject)ksp));
    154:     PetscLogEventBarrierEnd(VEC_ReduceBarrier,0,0,0,0,PetscObjectComm((PetscObject)ksp));
    155:     xi1  = outsums[0];
    156:     xi2  = outsums[1];
    157:     xi3  = outsums[2];
    158:     xi4  = outsums[3];

    160:     /* test denominator */
    161:     if (xi3 == 0.0) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_PLIB,"Divide by zero");
    162:     if (sigma == 0.0) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_PLIB,"Divide by zero");

    164:     /* scalar updates */
    165:     omega = xi2 / xi3;
    166:     beta  = -xi4 / sigma;
    167:     rho   = PetscSqrtReal(PetscAbsScalar(xi1 - omega * xi2)); /* residual norm */

    169:     /* vector updates */
    170:     VecAXPBYPCZ(X,alpha,omega,1.0,P2,S2); /* x <- alpha * p2 + omega * s2 + x */

    172:     /* convergence test */
    173:     PetscObjectSAWsTakeAccess((PetscObject)ksp);
    174:     ksp->its++;
    175:     ksp->rnorm = rho;
    176:     PetscObjectSAWsGrantAccess((PetscObject)ksp);
    177:     KSPLogResidualHistory(ksp,rho);
    178:     KSPMonitor(ksp,i+1,rho);
    179:     (*ksp->converged)(ksp,i+1,rho,&ksp->reason,ksp->cnvP);
    180:     if (ksp->reason) break;

    182:     /* vector updates */
    183:     PetscLogEventBegin(VEC_Ops,0,0,0,0);
    184:     for (j=0; j<N; j++) {
    185:       r[j] = s[j] - omega * t[j]; /* r <- s - omega t */
    186:       p[j] = r[j] + beta * (p[j] - omega * v[j]); /* p <- r + beta * (p - omega v) */
    187:     }
    188:     PetscLogFlops(6.0*N);
    189:     PetscLogEventEnd(VEC_Ops,0,0,0,0);

    191:   }

    193:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
    194:   return(0);
    195: }

    197: /*MC
    198:      KSPFBCGSR - Implements a mathematically equivalent variant of FBiCGSTab.

    200:    Options Database Keys:
    201: .   see KSPSolve()

    203:    Level: beginner

    205:    Notes: Only allow right preconditioning

    207: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP, KSPBICG, KSPFBCGSL, KSPSetPCSide()
    208: M*/
    211: PETSC_EXTERN PetscErrorCode KSPCreate_FBCGSR(KSP ksp)
    212: {
    214:   KSP_BCGS       *bcgs;

    217:   PetscNewLog(ksp,&bcgs);

    219:   ksp->data                = bcgs;
    220:   ksp->ops->setup          = KSPSetUp_FBCGSR;
    221:   ksp->ops->solve          = KSPSolve_FBCGSR;
    222:   ksp->ops->destroy        = KSPDestroy_BCGS;
    223:   ksp->ops->reset          = KSPReset_BCGS;
    224:   ksp->ops->buildsolution  = KSPBuildSolution_BCGS;
    225:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
    226:   ksp->ops->setfromoptions = KSPSetFromOptions_BCGS;
    227:   ksp->pc_side             = PC_RIGHT; /* set default PC side */

    229:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,3);
    230:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,2);
    231:   return(0);
    232: }