:orphan:
# PCShellSetApply
Sets routine to use as preconditioner.
## Synopsis
```
#include "petscpc.h"
PetscErrorCode PCShellSetApply(PC pc, PetscErrorCode (*apply)(PC, Vec, Vec))
```
Logically Collective
## Input Parameters
- ***pc -*** the preconditioner context
- ***apply -*** the application-provided preconditioning routine
## Calling sequence of `apply`
```none
PetscErrorCode apply(PC pc, Vec xin, Vec xout)
```
- ***pc -*** the preconditioner, get the application context with `PCShellGetContext()`
- ***xin -*** input vector
- ***xout -*** output vector
## See Also
`PCSHELL`, `PCShellSetApplyRichardson()`, `PCShellSetSetUp()`, `PCShellSetApplyTranspose()`, `PCShellSetContext()`, `PCShellSetApplyBA()`, `PCShellSetApplySymmetricRight()`, `PCShellSetApplySymmetricLeft()`
## Level
intermediate
## Location
src/ksp/pc/impls/shell/shellpc.c
## Examples
src/ksp/ksp/tutorials/ex15.c
src/ksp/ksp/tutorials/ex15f.F90
src/ksp/ksp/tutorials/ex60.c
src/snes/tutorials/ex3.c
src/tao/pde_constrained/tutorials/hyperbolic.c
src/tao/pde_constrained/tutorials/parabolic.c
## Implementations
PCShellSetApply_Shell(PC pc, PetscErrorCode (*apply) in src/ksp/pc/impls/shell/shellpc.c
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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/ksp/pc/impls/shell/shellpc.c)
[Index of all PC routines](index.md)
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[Index of all manual pages](/manualpages/singleindex.md)