Actual source code: groppcg.c

petsc-3.9.0 2018-04-07
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  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: {

 14:   KSPSetWorkVecs(ksp,6);
 15:   return(0);
 16: }

 18: /*
 19:  KSPSolve_GROPPCG

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

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

 39:   x = ksp->vec_sol;
 40:   b = ksp->vec_rhs;
 41:   r = ksp->work[0];
 42:   p = ksp->work[1];
 43:   s = ksp->work[2];
 44:   S = ksp->work[3];
 45:   z = ksp->work[4];
 46:   Z = ksp->work[5];

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

 50:   ksp->its = 0;
 51:   if (!ksp->guess_zero) {
 52:     KSP_MatMult(ksp,Amat,x,r);            /*     r <- b - Ax     */
 53:     VecAYPX(r,-1.0,b);
 54:   } else {
 55:     VecCopy(b,r);                         /*     r <- b (x is 0) */
 56:   }

 58:   KSP_PCApply(ksp,r,z);                   /*     z <- Br   */
 59:   VecCopy(z,p);                           /*     p <- z    */
 60:   VecDotBegin(r,z,&gamma);                  /*     gamma <- z'*r       */
 61:   PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)r));
 62:   KSP_MatMult(ksp,Amat,p,s);              /*     s <- Ap   */
 63:   VecDotEnd(r,z,&gamma);                  /*     gamma <- z'*r       */

 65:   switch (ksp->normtype) {
 66:   case KSP_NORM_PRECONDITIONED:
 67:     /* This could be merged with the computation of gamma above */
 68:     VecNorm(z,NORM_2,&dp);                /*     dp <- z'*z = e'*A'*B'*B*A'*e'     */
 69:     break;
 70:   case KSP_NORM_UNPRECONDITIONED:
 71:     /* This could be merged with the computation of gamma above */
 72:     VecNorm(r,NORM_2,&dp);                /*     dp <- r'*r = e'*A'*A*e            */
 73:     break;
 74:   case KSP_NORM_NATURAL:
 75:     KSPCheckDot(ksp,gamma);
 76:     dp = PetscSqrtReal(PetscAbsScalar(gamma));                  /*     dp <- r'*z = r'*B*r = e'*A'*B*A*e */
 77:     break;
 78:   case KSP_NORM_NONE:
 79:     dp = 0.0;
 80:     break;
 81:   default: SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"%s",KSPNormTypes[ksp->normtype]);
 82:   }
 83:   KSPLogResidualHistory(ksp,dp);
 84:   KSPMonitor(ksp,0,dp);
 85:   ksp->rnorm = dp;
 86:   (*ksp->converged)(ksp,0,dp,&ksp->reason,ksp->cnvP); /* test for convergence */
 87:   if (ksp->reason) return(0);

 89:   i = 0;
 90:   do {
 91:     ksp->its = i+1;
 92:     i++;

 94:     VecDotBegin(p,s,&t);
 95:     PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)p));

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

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

101:     alpha = gamma / t;
102:     VecAXPY(x, alpha,p);   /*     x <- x + alpha * p   */
103:     VecAXPY(r,-alpha,s);   /*     r <- r - alpha * s   */
104:     VecAXPY(z,-alpha,S);   /*     z <- z - alpha * S   */

106:     if (ksp->normtype == KSP_NORM_UNPRECONDITIONED) {
107:       VecNormBegin(r,NORM_2,&dp);
108:     } else if (ksp->normtype == KSP_NORM_PRECONDITIONED) {
109:       VecNormBegin(z,NORM_2,&dp);
110:     }
111:     VecDotBegin(r,z,&gammaNew);
112:     PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)r));

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

116:     if (ksp->normtype == KSP_NORM_UNPRECONDITIONED) {
117:       VecNormEnd(r,NORM_2,&dp);
118:     } else if (ksp->normtype == KSP_NORM_PRECONDITIONED) {
119:       VecNormEnd(z,NORM_2,&dp);
120:     }
121:     VecDotEnd(r,z,&gammaNew);

123:     if (ksp->normtype == KSP_NORM_NATURAL) {
124:       KSPCheckDot(ksp,gammaNew);
125:       dp = PetscSqrtReal(PetscAbsScalar(gammaNew));                  /*     dp <- r'*z = r'*B*r = e'*A'*B*A*e */
126:     } else if (ksp->normtype == KSP_NORM_NONE) {
127:       dp = 0.0;
128:     }
129:     ksp->rnorm = dp;
130:     KSPLogResidualHistory(ksp,dp);
131:     KSPMonitor(ksp,i,dp);
132:     (*ksp->converged)(ksp,i,dp,&ksp->reason,ksp->cnvP);
133:     if (ksp->reason) break;

135:     beta  = gammaNew / gamma;
136:     gamma = gammaNew;
137:     VecAYPX(p,beta,z);   /*     p <- z + beta * p   */
138:     VecAYPX(s,beta,Z);   /*     s <- Z + beta * s   */

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

142:   if (i >= ksp->max_it) ksp->reason = KSP_DIVERGED_ITS;
143:   return(0);
144: }

146: /*MC
147:    KSPGROPPCG - A pipelined conjugate gradient method from Bill Gropp

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

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

154:    Level: intermediate

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

160:    Contributed by:
161:    Pieter Ghysels, Universiteit Antwerpen, Intel Exascience lab Flanders

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

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

169: PETSC_EXTERN PetscErrorCode KSPCreate_GROPPCG(KSP ksp)
170: {

174:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_LEFT,2);
175:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,2);
176:   KSPSetSupportedNorm(ksp,KSP_NORM_NATURAL,PC_LEFT,2);
177:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,1);

179:   ksp->ops->setup          = KSPSetUp_GROPPCG;
180:   ksp->ops->solve          = KSPSolve_GROPPCG;
181:   ksp->ops->destroy        = KSPDestroyDefault;
182:   ksp->ops->view           = 0;
183:   ksp->ops->setfromoptions = 0;
184:   ksp->ops->buildsolution  = KSPBuildSolutionDefault;
185:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
186:   return(0);
187: }