/*$Id: preonly.c,v 1.42 2001/05/14 21:07:54 bsmith Exp $*/

/*                       
       This implements a stub method that applies ONLY the preconditioner.
       This may be used in inner iterations, where it is desired to 
       allow multiple iterations as well as the "0-iteration" case
*/
#include "src/sles/ksp/kspimpl.h"

#undef __FUNCT__  
#define __FUNCT__ "KSPSetUp_PREONLY"
static int KSPSetUp_PREONLY(KSP ksp)
{
  PetscFunctionBegin;
  PetscFunctionReturn(0);
}

#undef __FUNCT__  
#define __FUNCT__ "KSPSolve_PREONLY"
static int  KSPSolve_PREONLY(KSP ksp,int *its)
{
  int        ierr;
  Vec        X,B;
  PetscTruth diagonalscale;

  PetscFunctionBegin;
  ierr    = PCDiagonalScale(ksp->B,&diagonalscale);CHKERRQ(ierr);
  if (diagonalscale) SETERRQ1(1,"Krylov method %s does not support diagonal scaling",ksp->type_name);
  if (!ksp->guess_zero) {
    SETERRQ(1,"Running KSP of preonly doesn't make sense with nonzero initial guess\n\
               you probably want a KSP type of Richardson");
  }

  ksp->its    = 0;
  X           = ksp->vec_sol;
  B           = ksp->vec_rhs;
  ierr        = KSP_PCApply(ksp,ksp->B,B,X);CHKERRQ(ierr);
  *its        = 1;
  ksp->its    = 1;
  ksp->reason = KSP_CONVERGED_ITS;
  PetscFunctionReturn(0);
}

EXTERN_C_BEGIN
#undef __FUNCT__  
#define __FUNCT__ "KSPCreate_PREONLY"
int KSPCreate_PREONLY(KSP ksp)
{
  PetscFunctionBegin;
  ksp->data                      = (void*)0;
  ksp->ops->setup                = KSPSetUp_PREONLY;
  ksp->ops->solve                = KSPSolve_PREONLY;
  ksp->ops->destroy              = KSPDefaultDestroy;
  ksp->ops->buildsolution        = KSPDefaultBuildSolution;
  ksp->ops->buildresidual        = KSPDefaultBuildResidual;
  ksp->ops->setfromoptions       = 0;
  ksp->ops->view                 = 0;
  PetscFunctionReturn(0);
}
EXTERN_C_END