1: /*
  2:     Identity preconditioner, simply copies vector x to y.
  3: */
  4: #include <petsc/private/pcimpl.h>

  6: static PetscErrorCode PCApply_None(PC pc, Vec x, Vec y)
  7: {
  8:   PetscFunctionBegin;
  9:   PetscCall(VecCopy(x, y));
 10:   PetscFunctionReturn(PETSC_SUCCESS);
 11: }

 13: static PetscErrorCode PCMatApply_None(PC pc, Mat X, Mat Y)
 14: {
 15:   PetscFunctionBegin;
 16:   PetscCall(MatCopy(X, Y, SAME_NONZERO_PATTERN));
 17:   PetscFunctionReturn(PETSC_SUCCESS);
 18: }

 20: /*MC
 21:      PCNONE - This is used when you wish to employ a nonpreconditioned
 22:              Krylov method.

 24:    Level: beginner

 26:   Developer Note:
 27:   This is implemented by a `VecCopy()`. It would be nice if the `KSP` implementations could be organized to avoid this copy without making them
 28:   more complex.

 30: .seealso: [](ch_ksp), `PCCreate()`, `PCSetType()`, `PCType`, `PC`
 31: M*/

 33: PETSC_EXTERN PetscErrorCode PCCreate_None(PC pc)
 34: {
 35:   PetscFunctionBegin;
 36:   pc->ops->apply               = PCApply_None;
 37:   pc->ops->matapply            = PCMatApply_None;
 38:   pc->ops->applytranspose      = PCApply_None;
 39:   pc->ops->destroy             = NULL;
 40:   pc->ops->setup               = NULL;
 41:   pc->ops->view                = NULL;
 42:   pc->ops->applysymmetricleft  = PCApply_None;
 43:   pc->ops->applysymmetricright = PCApply_None;

 45:   pc->data = NULL;
 46:   PetscFunctionReturn(PETSC_SUCCESS);
 47: }