Actual source code: pipecr.c

petsc-master 2020-07-04
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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
 21: */
 22: static PetscErrorCode  KSPSolve_PIPECR(KSP ksp)
 23: {
 25:   PetscInt       i;
 26:   PetscScalar    alpha=0.0,beta=0.0,gamma,gammaold=0.0,delta;
 27:   PetscReal      dp   = 0.0;
 28:   Vec            X,B,Z,P,W,Q,U,M,N;
 29:   Mat            Amat,Pmat;
 30:   PetscBool      diagonalscale;

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

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

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

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

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

 77:   i = 0;
 78:   do {
 79:     KSP_PCApply(ksp,W,M);            /*   m <- Bw       */

 81:     if (i > 0 && ksp->normtype == KSP_NORM_PRECONDITIONED) {
 82:       VecNormBegin(U,NORM_2,&dp);
 83:     }
 84:     VecDotBegin(W,U,&gamma);
 85:     VecDotBegin(M,W,&delta);
 86:     PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)U));

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

 90:     if (i > 0 && ksp->normtype == KSP_NORM_PRECONDITIONED) {
 91:       VecNormEnd(U,NORM_2,&dp);
 92:     }
 93:     VecDotEnd(W,U,&gamma);
 94:     VecDotEnd(M,W,&delta);

 96:     if (i > 0) {
 97:       if (ksp->normtype == KSP_NORM_NONE) dp = 0.0;
 98:       ksp->rnorm = dp;
 99:       KSPLogResidualHistory(ksp,dp);
100:       KSPMonitor(ksp,i,dp);
101:       (*ksp->converged)(ksp,i,dp,&ksp->reason,ksp->cnvP);
102:       if (ksp->reason) return(0);
103:     }

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

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

131:   } while (i<=ksp->max_it);
132:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
133:   return(0);
134: }

136: /*MC
137:    KSPPIPECR - Pipelined conjugate residual method

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

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

144:    Level: intermediate

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

150:    Contributed by:
151:    Pieter Ghysels, Universiteit Antwerpen, Intel Exascience lab Flanders

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

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

160: PETSC_EXTERN PetscErrorCode KSPCreate_PIPECR(KSP ksp)
161: {

165:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,2);
166:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,1);

168:   ksp->ops->setup          = KSPSetUp_PIPECR;
169:   ksp->ops->solve          = KSPSolve_PIPECR;
170:   ksp->ops->destroy        = KSPDestroyDefault;
171:   ksp->ops->view           = NULL;
172:   ksp->ops->setfromoptions = NULL;
173:   ksp->ops->buildsolution  = KSPBuildSolutionDefault;
174:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
175:   return(0);
176: }