2: #include <petsc-private/kspimpl.h>

  6: static PetscErrorCode KSPSetUp_PREONLY(KSP ksp)
  7: {
  9:   return(0);
 10: }

 14: static PetscErrorCode  KSPSolve_PREONLY(KSP ksp)
 15: {
 17:   PetscBool      diagonalscale;

 20:   PCGetDiagonalScale(ksp->pc,&diagonalscale);
 21:   if (diagonalscale) SETERRQ1(((PetscObject)ksp)->comm,PETSC_ERR_SUP,"Krylov method %s does not support diagonal scaling",((PetscObject)ksp)->type_name);
 22:   if (!ksp->guess_zero) SETERRQ(((PetscObject)ksp)->comm,PETSC_ERR_USER,"Running KSP of preonly doesn't make sense with nonzero initial guess\n\
 23:                you probably want a KSP type of Richardson");
 24:   ksp->its    = 0;
 25:   PCSetInitialGuessNonzero(ksp->pc,(PetscBool)!(int)ksp->guess_zero);
 26:   KSP_PCApply(ksp,ksp->vec_rhs,ksp->vec_sol);
 27:   ksp->its    = 1;
 28:   ksp->reason = KSP_CONVERGED_ITS;
 29:   return(0);
 30: }

 32: /*MC
 33:      KSPPREONLY - This implements a stub method that applies ONLY the preconditioner.
 34:                   This may be used in inner iterations, where it is desired to 
 35:                   allow multiple iterations as well as the "0-iteration" case. It is 
 36:                   commonly used with the direct solver preconditioners like PCLU and PCCHOLESKY

 38:    Options Database Keys:
 39: .   see KSPSolve()

 41:    Level: beginner

 43: .seealso:  KSPCreate(), KSPSetType(), KSPType (for list of available types), KSP

 45: M*/

 47: EXTERN_C_BEGIN
 50: PetscErrorCode  KSPCreate_PREONLY(KSP ksp)
 51: {

 55:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,2); /* LEFT/RIGHT is arbitrary, so "support" both */
 56:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_RIGHT,1);
 57:   ksp->data                      = (void*)0;
 58:   ksp->ops->setup                = KSPSetUp_PREONLY;
 59:   ksp->ops->solve                = KSPSolve_PREONLY;
 60:   ksp->ops->destroy              = KSPDefaultDestroy;
 61:   ksp->ops->buildsolution        = KSPDefaultBuildSolution;
 62:   ksp->ops->buildresidual        = KSPDefaultBuildResidual;
 63:   ksp->ops->setfromoptions       = 0;
 64:   ksp->ops->view                 = 0;
 65:   return(0);
 66: }
 67: EXTERN_C_END