Actual source code: pipecr.c

petsc-3.8.3 2017-12-09
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  1:  #include <petsc/private/kspimpl.h>

  3: /*
  4:      KSPSetUp_PIPECR - Sets up the workspace needed by the PIPECR method.

  6:       This is called once, usually automatically by KSPSolve() or KSPSetUp()
  7:      but can be called directly by KSPSetUp()
  8: */
  9: static PetscErrorCode KSPSetUp_PIPECR(KSP ksp)
 10: {

 14:   /* get work vectors needed by PIPECR */
 15:   KSPSetWorkVecs(ksp,7);
 16:   return(0);
 17: }

 19: /*
 20:  KSPSolve_PIPECR - This routine actually applies the pipelined conjugate residual method

 22:  Input Parameter:
 23:  .     ksp - the Krylov space object that was set to use conjugate gradient, by, for
 24:              example, KSPCreate(MPI_Comm,KSP *ksp); KSPSetType(ksp,KSPCG);
 25: */
 26: static PetscErrorCode  KSPSolve_PIPECR(KSP ksp)
 27: {
 29:   PetscInt       i;
 30:   PetscScalar    alpha=0.0,beta=0.0,gamma,gammaold=0.0,delta;
 31:   PetscReal      dp   = 0.0;
 32:   Vec            X,B,Z,P,W,Q,U,M,N;
 33:   Mat            Amat,Pmat;
 34:   PetscBool      diagonalscale;

 37:   PCGetDiagonalScale(ksp->pc,&diagonalscale);
 38:   if (diagonalscale) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"Krylov method %s does not support diagonal scaling",((PetscObject)ksp)->type_name);

 40:   X = ksp->vec_sol;
 41:   B = ksp->vec_rhs;
 42:   M = ksp->work[0];
 43:   Z = ksp->work[1];
 44:   P = ksp->work[2];
 45:   N = ksp->work[3];
 46:   W = ksp->work[4];
 47:   Q = ksp->work[5];
 48:   U = ksp->work[6];

 50:   PCGetOperators(ksp->pc,&Amat,&Pmat);

 52:   ksp->its = 0;
 53:   /* we don't have an R vector, so put the (unpreconditioned) residual in w for now */
 54:   if (!ksp->guess_zero) {
 55:     KSP_MatMult(ksp,Amat,X,W);            /*     w <- b - Ax     */
 56:     VecAYPX(W,-1.0,B);
 57:   } else {
 58:     VecCopy(B,W);                         /*     w <- b (x is 0) */
 59:   }
 60:   KSP_PCApply(ksp,W,U);                   /*     u <- Bw   */

 62:   switch (ksp->normtype) {
 63:   case KSP_NORM_PRECONDITIONED:
 64:     VecNormBegin(U,NORM_2,&dp);           /*     dp <- u'*u = e'*A'*B'*B*A'*e'     */
 65:     PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)U));
 66:     KSP_MatMult(ksp,Amat,U,W);            /*     w <- Au   */
 67:     VecNormEnd(U,NORM_2,&dp);
 68:     break;
 69:   case KSP_NORM_NONE:
 70:     KSP_MatMult(ksp,Amat,U,W);
 71:     dp   = 0.0;
 72:     break;
 73:   default: SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"%s",KSPNormTypes[ksp->normtype]);
 74:   }
 75:   KSPLogResidualHistory(ksp,dp);
 76:   KSPMonitor(ksp,0,dp);
 77:   ksp->rnorm = dp;
 78:   (*ksp->converged)(ksp,0,dp,&ksp->reason,ksp->cnvP); /* test for convergence */
 79:   if (ksp->reason) return(0);

 81:   i = 0;
 82:   do {
 83:     KSP_PCApply(ksp,W,M);            /*   m <- Bw       */

 85:     if (i > 0 && ksp->normtype == KSP_NORM_PRECONDITIONED) {
 86:       VecNormBegin(U,NORM_2,&dp);
 87:     }
 88:     VecDotBegin(W,U,&gamma);
 89:     VecDotBegin(M,W,&delta);
 90:     PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)U));

 92:     KSP_MatMult(ksp,Amat,M,N);       /*   n <- Am       */

 94:     if (i > 0 && ksp->normtype == KSP_NORM_PRECONDITIONED) {
 95:       VecNormEnd(U,NORM_2,&dp);
 96:     }
 97:     VecDotEnd(W,U,&gamma);
 98:     VecDotEnd(M,W,&delta);

100:     if (i > 0) {
101:       if (ksp->normtype == KSP_NORM_NONE) dp = 0.0;
102:       ksp->rnorm = dp;
103:       KSPLogResidualHistory(ksp,dp);
104:       KSPMonitor(ksp,i,dp);
105:       (*ksp->converged)(ksp,i,dp,&ksp->reason,ksp->cnvP);
106:       if (ksp->reason) break;
107:     }

109:     if (i == 0) {
110:       alpha = gamma / delta;
111:       VecCopy(N,Z);        /*     z <- n          */
112:       VecCopy(M,Q);        /*     q <- m          */
113:       VecCopy(U,P);        /*     p <- u          */
114:     } else {
115:       beta  = gamma / gammaold;
116:       alpha = gamma / (delta - beta / alpha * gamma);
117:       VecAYPX(Z,beta,N);   /*     z <- n + beta * z   */
118:       VecAYPX(Q,beta,M);   /*     q <- m + beta * q   */
119:       VecAYPX(P,beta,U);   /*     p <- u + beta * p   */
120:     }
121:     VecAXPY(X, alpha,P); /*     x <- x + alpha * p   */
122:     VecAXPY(U,-alpha,Q); /*     u <- u - alpha * q   */
123:     VecAXPY(W,-alpha,Z); /*     w <- w - alpha * z   */
124:     gammaold = gamma;
125:     i++;
126:     ksp->its = i;

128:     /* if (i%50 == 0) { */
129:     /*   KSP_MatMult(ksp,Amat,X,W);            /\*     w <- b - Ax     *\/ */
130:     /*   VecAYPX(W,-1.0,B); */
131:     /*   KSP_PCApply(ksp,W,U); */
132:     /*   KSP_MatMult(ksp,Amat,U,W); */
133:     /* } */

135:   } while (i<ksp->max_it);
136:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
137:   return(0);
138: }

140: /*MC
141:    KSPPIPECR - Pipelined conjugate residual method

143:    This method has only a single non-blocking reduction per iteration, compared to 2 blocking for standard CR.  The
144:    non-blocking reduction is overlapped by the matrix-vector product, but not the preconditioner application.

146:    See also KSPPIPECG, where the reduction is only overlapped with the matrix-vector product.

148:    Level: intermediate

150:    Notes:
151:    MPI configuration may be necessary for reductions to make asynchronous progress, which is important for performance of pipelined methods.
152:    See the FAQ on the PETSc website for details.

154:    Contributed by:
155:    Pieter Ghysels, Universiteit Antwerpen, Intel Exascience lab Flanders

157:    Reference:
158:    P. Ghysels and W. Vanroose, "Hiding global synchronization latency in the preconditioned Conjugate Gradient algorithm",
159:    Submitted to Parallel Computing, 2012.

161: .seealso: KSPCreate(), KSPSetType(), KSPPIPECG, KSPGROPPCG, KSPPGMRES, KSPCG, KSPCGUseSingleReduction()
162: M*/

164: PETSC_EXTERN PetscErrorCode KSPCreate_PIPECR(KSP ksp)
165: {

169:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,2);
170:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,1);

172:   ksp->ops->setup          = KSPSetUp_PIPECR;
173:   ksp->ops->solve          = KSPSolve_PIPECR;
174:   ksp->ops->destroy        = KSPDestroyDefault;
175:   ksp->ops->view           = 0;
176:   ksp->ops->setfromoptions = 0;
177:   ksp->ops->buildsolution  = KSPBuildSolutionDefault;
178:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
179:   return(0);
180: }