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# MatMFFDSetFunctioniBase
Sets the base vector for a single component function evaluation for a `MATMFFD` matrix 
## Synopsis
```
#include "petscmat.h"   
PetscErrorCode MatMFFDSetFunctioniBase(Mat mat, PetscErrorCode (*func)(void *, Vec))
```
Logically Collective


## Input Parameters

- ***mat -*** the `MATMFFD` matrix free matrix
- ***func -*** the function to use





## Notes
If you use this you MUST call `MatAssemblyBegin()` and `MatAssemblyEnd()` on the matrix free
matrix inside your compute Jacobian routine.

This function is necessary to compute the diagonal of the matrix, used for example with `PCJACOBI`


## See Also
 [](ch_matrices), `Mat`, `MATMFFD`, `MatCreateSNESMF()`, `MatMFFDGetH()`, `MatCreateMFFD()`, `MATMFFD`
`MatMFFDSetHHistory()`, `MatMFFDResetHHistory()`, `SNESetFunction()`, `MatGetDiagonal()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/mffd/mffd.c.html#MatMFFDSetFunctioniBase">src/mat/impls/mffd/mffd.c</A>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/mffd/mffd.c.html#MatMFFDSetFunctioniBase_MFFD">MatMFFDSetFunctioniBase_MFFD in src/mat/impls/mffd/mffd.c</A><BR>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/mat/impls/mffd/mffd.c)


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