# PCShellSetMatApply
Sets routine to use as preconditioner on a block of vectors. 
## Synopsis
```
#include "petscpc.h" 
PetscErrorCode PCShellSetMatApply(PC pc, PetscErrorCode (*matapply)(PC, Mat, Mat))
```
Logically Collective


## Input Parameters

- ***pc -*** the preconditioner context
- ***apply -*** the application-provided preconditioning routine



## Calling sequence of apply
```none
   PetscErrorCode apply (PC pc,Mat Xin,Mat Xout)
```



- ***pc -*** the preconditioner, get the application context with PCShellGetContext()
- ***Xin -*** input block of vectors
- ***Xout -*** output block of vectors



## Note
The function MUST return an error code of 0 on success and nonzero on failure.




## See Also
 `PCSHELL`, `PCShellSetApply()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/shell/shellpc.c.html#PCShellSetMatApply">src/ksp/pc/impls/shell/shellpc.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex79.c.html">src/ksp/ksp/tutorials/ex79.c.html</A><BR>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/shell/shellpc.c.html#PCShellSetMatApply_Shell(PC pc, PetscErrorCode (*matapply)">PCShellSetMatApply_Shell(PC pc, PetscErrorCode (*matapply) in src/ksp/pc/impls/shell/shellpc.c</A><BR>


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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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