Actual source code: groppcg.c

  1: #include <petsc/private/kspimpl.h>

  3: /*
  4:  KSPSetUp_GROPPCG - Sets up the workspace needed by the GROPPCG 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_GROPPCG(KSP ksp)
 10: {
 11:   KSPSetWorkVecs(ksp,6);
 12:   return 0;
 13: }

 15: /*
 16:  KSPSolve_GROPPCG

 18:  Input Parameter:
 19:  .     ksp - the Krylov space object that was set to use conjugate gradient, by, for
 20:              example, KSPCreate(MPI_Comm,KSP *ksp); KSPSetType(ksp,KSPCG);
 21: */
 22: static PetscErrorCode  KSPSolve_GROPPCG(KSP ksp)
 23: {
 24:   PetscInt       i;
 25:   PetscScalar    alpha,beta = 0.0,gamma,gammaNew,t;
 26:   PetscReal      dp = 0.0;
 27:   Vec            x,b,r,p,s,S,z,Z;
 28:   Mat            Amat,Pmat;
 29:   PetscBool      diagonalscale;

 31:   PCGetDiagonalScale(ksp->pc,&diagonalscale);

 34:   x = ksp->vec_sol;
 35:   b = ksp->vec_rhs;
 36:   r = ksp->work[0];
 37:   p = ksp->work[1];
 38:   s = ksp->work[2];
 39:   S = ksp->work[3];
 40:   z = ksp->work[4];
 41:   Z = ksp->work[5];

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

 45:   ksp->its = 0;
 46:   if (!ksp->guess_zero) {
 47:     KSP_MatMult(ksp,Amat,x,r);            /*     r <- b - Ax     */
 48:     VecAYPX(r,-1.0,b);
 49:   } else {
 50:     VecCopy(b,r);                         /*     r <- b (x is 0) */
 51:   }

 53:   KSP_PCApply(ksp,r,z);                   /*     z <- Br   */
 54:   VecCopy(z,p);                           /*     p <- z    */
 55:   VecDotBegin(r,z,&gamma);                  /*     gamma <- z'*r       */
 56:   PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)r));
 57:   KSP_MatMult(ksp,Amat,p,s);              /*     s <- Ap   */
 58:   VecDotEnd(r,z,&gamma);                  /*     gamma <- z'*r       */

 60:   switch (ksp->normtype) {
 61:   case KSP_NORM_PRECONDITIONED:
 62:     /* This could be merged with the computation of gamma above */
 63:     VecNorm(z,NORM_2,&dp);                /*     dp <- z'*z = e'*A'*B'*B*A'*e'     */
 64:     break;
 65:   case KSP_NORM_UNPRECONDITIONED:
 66:     /* This could be merged with the computation of gamma above */
 67:     VecNorm(r,NORM_2,&dp);                /*     dp <- r'*r = e'*A'*A*e            */
 68:     break;
 69:   case KSP_NORM_NATURAL:
 70:     KSPCheckDot(ksp,gamma);
 71:     dp = PetscSqrtReal(PetscAbsScalar(gamma));                  /*     dp <- r'*z = r'*B*r = e'*A'*B*A*e */
 72:     break;
 73:   case KSP_NORM_NONE:
 74:     dp = 0.0;
 75:     break;
 76:   default: SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"%s",KSPNormTypes[ksp->normtype]);
 77:   }
 78:   KSPLogResidualHistory(ksp,dp);
 79:   KSPMonitor(ksp,0,dp);
 80:   ksp->rnorm = dp;
 81:   (*ksp->converged)(ksp,0,dp,&ksp->reason,ksp->cnvP); /* test for convergence */
 82:   if (ksp->reason) return 0;

 84:   i = 0;
 85:   do {
 86:     ksp->its = i+1;
 87:     i++;

 89:     VecDotBegin(p,s,&t);
 90:     PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)p));

 92:     KSP_PCApply(ksp,s,S);         /*   S <- Bs       */

 94:     VecDotEnd(p,s,&t);

 96:     alpha = gamma / t;
 97:     VecAXPY(x, alpha,p);   /*     x <- x + alpha * p   */
 98:     VecAXPY(r,-alpha,s);   /*     r <- r - alpha * s   */
 99:     VecAXPY(z,-alpha,S);   /*     z <- z - alpha * S   */

101:     if (ksp->normtype == KSP_NORM_UNPRECONDITIONED) {
102:       VecNormBegin(r,NORM_2,&dp);
103:     } else if (ksp->normtype == KSP_NORM_PRECONDITIONED) {
104:       VecNormBegin(z,NORM_2,&dp);
105:     }
106:     VecDotBegin(r,z,&gammaNew);
107:     PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)r));

109:     KSP_MatMult(ksp,Amat,z,Z);      /*   Z <- Az       */

111:     if (ksp->normtype == KSP_NORM_UNPRECONDITIONED) {
112:       VecNormEnd(r,NORM_2,&dp);
113:     } else if (ksp->normtype == KSP_NORM_PRECONDITIONED) {
114:       VecNormEnd(z,NORM_2,&dp);
115:     }
116:     VecDotEnd(r,z,&gammaNew);

118:     if (ksp->normtype == KSP_NORM_NATURAL) {
119:       KSPCheckDot(ksp,gammaNew);
120:       dp = PetscSqrtReal(PetscAbsScalar(gammaNew));                  /*     dp <- r'*z = r'*B*r = e'*A'*B*A*e */
121:     } else if (ksp->normtype == KSP_NORM_NONE) {
122:       dp = 0.0;
123:     }
124:     ksp->rnorm = dp;
125:     KSPLogResidualHistory(ksp,dp);
126:     KSPMonitor(ksp,i,dp);
127:     (*ksp->converged)(ksp,i,dp,&ksp->reason,ksp->cnvP);
128:     if (ksp->reason) return 0;

130:     beta  = gammaNew / gamma;
131:     gamma = gammaNew;
132:     VecAYPX(p,beta,z);   /*     p <- z + beta * p   */
133:     VecAYPX(s,beta,Z);   /*     s <- Z + beta * s   */

135:   } while (i<ksp->max_it);

137:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
138:   return 0;
139: }

141: PETSC_INTERN PetscErrorCode KSPBuildResidual_CG(KSP,Vec,Vec,Vec*);

143: /*MC
144:    KSPGROPPCG - A pipelined conjugate gradient method from Bill Gropp

146:    This method has two reductions, one of which is overlapped with the matrix-vector product and one of which is
147:    overlapped with the preconditioner.

149:    See also KSPPIPECG, which has only a single reduction that overlaps both the matrix-vector product and the preconditioner.

151:    Level: intermediate

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

157:    Contributed by:
158:    Pieter Ghysels, Universiteit Antwerpen, Intel Exascience lab Flanders

160:    Reference:
161:    http://www.cs.uiuc.edu/~wgropp/bib/talks/tdata/2012/icerm.pdf

163: .seealso: KSPCreate(), KSPSetType(), KSPPIPECG, KSPPIPECR, KSPPGMRES, KSPCG, KSPCGUseSingleReduction()
164: M*/

166: PETSC_EXTERN PetscErrorCode KSPCreate_GROPPCG(KSP ksp)
167: {
168:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_LEFT,2);
169:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,2);
170:   KSPSetSupportedNorm(ksp,KSP_NORM_NATURAL,PC_LEFT,2);
171:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,1);

173:   ksp->ops->setup          = KSPSetUp_GROPPCG;
174:   ksp->ops->solve          = KSPSolve_GROPPCG;
175:   ksp->ops->destroy        = KSPDestroyDefault;
176:   ksp->ops->view           = NULL;
177:   ksp->ops->setfromoptions = NULL;
178:   ksp->ops->buildsolution  = KSPBuildSolutionDefault;
179:   ksp->ops->buildresidual  = KSPBuildResidual_CG;
180:   return 0;
181: }