# PCPatchSetComputeOperator
Set the callback used to compute patch matrices 
## Synopsis
```
#include "petscpc.h" 
#include "petscmat.h" 
PetscErrorCode PCPatchSetComputeOperator(PC pc, PetscErrorCode (*func)(PC, PetscInt, Vec, Mat, IS, PetscInt, const PetscInt *, const PetscInt *, void *), void *ctx)
```
Logically collective


## Input Parameters

- ***pc   -*** The PC
- ***func -*** The callback
- ***ctx  -*** The user context



## Calling sequence of func
```none
func (PC pc,PetscInt point,Vec x,Mat mat,IS facetIS,PetscInt n,const PetscInt* dofsArray,const PetscInt* dofsArrayWithAll,void* ctx)
```


- ***pc               -*** The PC
- ***point            -*** The point
- ***x                -*** The input solution (not used in linear problems)
- ***mat              -*** The patch matrix
- ***cellIS           -*** An array of the cell numbers
- ***n                -*** The size of dofsArray
- ***dofsArray        -*** The dofmap for the dofs to be solved for
- ***dofsArrayWithAll -*** The dofmap for all dofs on the patch
- ***ctx              -*** The user context





## Note
The matrix entries have been set to zero before the call.


## See Also
 `PCPatchGetComputeOperator()`, `PCPatchSetComputeFunction()`, `PCPatchSetDiscretisationInfo()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/patch/pcpatch.c.html#PCPatchSetComputeOperator">src/ksp/pc/impls/patch/pcpatch.c</A>


---
[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/ksp/pc/impls/patch/pcpatch.c)


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