# SNESLineSearchSetVIFunctions
Sets VI-specific functions for line search computation. 
## Synopsis
```
#include "petscsnes.h" 
PetscErrorCode SNESLineSearchSetVIFunctions(SNESLineSearch linesearch, SNESLineSearchVIProjectFunc projectfunc, SNESLineSearchVINormFunc normfunc)
```
Logically Collective


## Input Parameters

- ***snes -*** nonlinear context obtained from `SNESCreate()`
- ***projectfunc -*** function for projecting the function to the bounds
- ***normfunc -*** function for computing the norm of an active set



## Calling sequence of projectfunc
```none
   projectfunc (SNES snes, Vec X)
```



## Input parameters for projectfunc

- ***snes -*** nonlinear context
- ***X -*** current solution



## Output parameter for projectfunc

- ***X -*** Projected solution



## Calling sequence of normfunc
```none
   projectfunc (SNES snes, Vec X, Vec F, PetscScalar * fnorm)
```



## Input parameters for normfunc

- ***snes -*** nonlinear context
- ***X -*** current solution
- ***F -*** current residual



## Output parameter for normfunc

- ***fnorm -*** VI-specific norm of the function



## Note
The VI solvers require projection of the solution to the feasible set.  projectfunc should implement this.

The VI solvers require special evaluation of the function norm such that the norm is only calculated
on the inactive set.  This should be implemented by normfunc.




## See Also
 `SNESLineSearch`, `SNESLineSearchGetVIFunctions()`, `SNESLineSearchSetPostCheck()`, `SNESLineSearchSetPreCheck()`

## Level
advanced

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


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