:orphan:
# SNESLineSearchShellSetUserFunc
Sets the user function for the `SNESLINESEARCHSHELL` implementation. 
## Synopsis
```
PetscErrorCode SNESLineSearchShellSetUserFunc(SNESLineSearch linesearch, SNESLineSearchUserFunc func, void *ctx)
```
Not Collective


## Input Parameters

- ***linesearch -*** `SNESLineSearch` context
- ***func -*** function implementing the linesearch shell.
- ***ctx -*** context for func



## Calling sequence of `func`
```none
PetscErrorCode func(SNESLinesearch, void *ctx)
```

- ***linesearch -*** the linesearch instance
- ***ctx -*** the above mentioned context



## Usage
```none
  PetscErrorCode shellfunc(SNESLineSearch linesearch,void * ctx)
  {
     Vec  X,Y,F,W,G;
     SNES snes;
     PetscFunctionBegin;
     PetscCall(SNESLineSearchGetSNES(linesearch,&snes));
     PetscCall(SNESLineSearchSetReason(linesearch,SNES_LINESEARCH_SUCCEEDED));
     PetscCall(SNESLineSearchGetVecs(linesearch,&X,&F,&Y,&W,&G));
     .. determine lambda using W and G as work vecs..
     PetscCall(VecAXPY(X,-lambda,Y));
     PetscCall(SNESComputeFunction(snes,X,F));
     PetscCall(SNESLineSearchComputeNorms(linesearch));
     PetscFunctionReturn(PETSC_SUCCESS);
  }

  ...

  PetscCall(SNESGetLineSearch(snes, &linesearch));
  PetscCall(SNESLineSearchSetType(linesearch, SNESLINESEARCHSHELL));
  PetscCall(SNESLineSearchShellSetUserFunc(linesearch, shellfunc, NULL));
```





## See Also
 `SNESLineSearchShellGetUserFunc()`, `SNESLINESEARCHSHELL`, `SNESLineSearchType`, `SNESLineSearch`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/linesearch/impls/shell/linesearchshell.c.html#SNESLineSearchShellSetUserFunc">src/snes/linesearch/impls/shell/linesearchshell.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex1f.F90.html">src/snes/tutorials/ex1f.F90</A><BR>


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


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