# SNESComputeMFFunction
Calls the function that has been set with `SNESSetMFFunction()`. 
## Synopsis
```
#include "petscsnes.h"  
PetscErrorCode SNESComputeMFFunction(SNES snes, Vec x, Vec y)
```
Collective on snes


## Input Parameters

- ***snes -*** the `SNES` context
- ***x -*** input vector



## Output Parameter

- ***y -*** function vector, as set by `SNESSetMFFunction()`



## Notes
`SNESComputeMFFunction()` is used within the matrix vector products called by the matrix created with `MatCreateSNESMF()`
so users would not generally call this routine themselves.

Since this function is intended for use with finite differencing it does not subtract the right hand side vector provided with `SNESSolve()`
while `SNESComputeFunction()` does. As such, this routine cannot be used with  `MatMFFDSetBase()` with a provided F function value even if it applies the
same function as `SNESComputeFunction()` if a `SNESSolve()` right hand side vector is use because the two functions difference would include this right hand side function.




## See Also
 `SNES`, `SNESSetFunction()`, `SNESGetFunction()`, `SNESComputeFunction()`, `MatCreateSNESMF`

## Level
developer

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/interface/snes.c.html#SNESComputeMFFunction">src/snes/interface/snes.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/snes/interface/snes.c)


[Index of all SNES routines](index.md)  
[Table of Contents for all manual pages](/docs/manualpages/index.md)  
[Index of all manual pages](/docs/manualpages/singleindex.md)  
