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

  4: static PetscErrorCode KSPSetUp_PREONLY(KSP ksp)
  5: {
  7:   return(0);
  8: }

 10: static PetscErrorCode  KSPSolve_PREONLY(KSP ksp)
 11: {
 13:   PetscBool      diagonalscale;
 14:   PCFailedReason pcreason;

 17:   PCGetDiagonalScale(ksp->pc,&diagonalscale);
 18:   if (diagonalscale) SETERRQ1(PetscObjectComm((PetscObject)ksp),PETSC_ERR_SUP,"Krylov method %s does not support diagonal scaling",((PetscObject)ksp)->type_name);
 19:   if (!ksp->guess_zero) SETERRQ(PetscObjectComm((PetscObject)ksp),PETSC_ERR_USER,"Running KSP of preonly doesn't make sense with nonzero initial guess\n\
 20:                you probably want a KSP type of Richardson");
 21:   ksp->its = 0;
 22:   KSP_PCApply(ksp,ksp->vec_rhs,ksp->vec_sol);
 23:   PCGetSetUpFailedReason(ksp->pc,&pcreason);
 24:   if (pcreason) {
 25:     ksp->reason = KSP_DIVERGED_PCSETUP_FAILED;
 26:   } else {
 27:     ksp->its    = 1;
 28:     ksp->reason = KSP_CONVERGED_ITS;
 29:   }
 30:   return(0);
 31: }

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

 39:    Options Database Keys:
 40: .   -ksp_type preonly

 42:    Level: beginner

 44:    Notes: Since this does not involve an iteration the basic KSP parameters such as tolerances and iteration counts
 45:           do not apply

 47:    Developer Notes: Even though this method does not use any norms, the user is allowed to set the KSPNormType to any value.
 48:     This is so the users does not have to change KSPNormType options when they switch from other KSP methods to this one.

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

 52: M*/

 54: PETSC_EXTERN PetscErrorCode KSPCreate_PREONLY(KSP ksp)
 55: {

 59:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_LEFT,3);
 60:   KSPSetSupportedNorm(ksp,KSP_NORM_NONE,PC_RIGHT,2);
 61:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_LEFT,2);
 62:   KSPSetSupportedNorm(ksp,KSP_NORM_PRECONDITIONED,PC_RIGHT,2);
 63:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_LEFT,2);
 64:   KSPSetSupportedNorm(ksp,KSP_NORM_UNPRECONDITIONED,PC_RIGHT,2);
 65:   KSPSetSupportedNorm(ksp,KSP_NORM_NATURAL,PC_LEFT,2);

 67:   ksp->data                = NULL;
 68:   ksp->ops->setup          = KSPSetUp_PREONLY;
 69:   ksp->ops->solve          = KSPSolve_PREONLY;
 70:   ksp->ops->destroy        = KSPDestroyDefault;
 71:   ksp->ops->buildsolution  = KSPBuildSolutionDefault;
 72:   ksp->ops->buildresidual  = KSPBuildResidualDefault;
 73:   ksp->ops->setfromoptions = 0;
 74:   ksp->ops->view           = 0;
 75:   return(0);
 76: }