# SNESSetFunction
Sets the function evaluation routine and function vector for use by the `SNES` routines in solving systems of nonlinear equations. 
## Synopsis
```
#include "petscsnes.h"  
PetscErrorCode SNESSetFunction(SNES snes, Vec r, PetscErrorCode (*f)(SNES, Vec, Vec, void *), void *ctx)
```
Logically Collective on snes


## Input Parameters

- ***snes -*** the `SNES` context
- ***r -*** vector to store function values, may be NULL
- ***f -*** function evaluation routine; see `SNESFunction` for calling sequence details
- ***ctx -*** [optional] user-defined context for private data for the
function evaluation routine (may be NULL)





## See Also
 `SNES`, `SNESGetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESSetPicard()`, `SNESFunction`

## Level
beginner

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

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex1.c.html">src/snes/tutorials/ex1.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex14.c.html">src/snes/tutorials/ex14.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex15.c.html">src/snes/tutorials/ex15.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex18.c.html">src/snes/tutorials/ex18.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex1f.F90.html">src/snes/tutorials/ex1f.F90.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex2.c.html">src/snes/tutorials/ex2.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex21.c.html">src/snes/tutorials/ex21.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex22.c.html">src/snes/tutorials/ex22.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex28.c.html">src/snes/tutorials/ex28.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex3.c.html">src/snes/tutorials/ex3.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex31.c.html">src/snes/tutorials/ex31.c.html</A><BR>


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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)  
