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# TaoLineSearchSetObjectiveAndGradientRoutine
Sets the objective/gradient evaluation routine for the line search 
## Synopsis
```
#include "petsctaolinesearch.h" 
PetscErrorCode TaoLineSearchSetObjectiveAndGradientRoutine(TaoLineSearch ls, PetscErrorCode (*func)(TaoLineSearch ls, Vec x, PetscReal *, Vec g, void *), void *ctx)
```
Logically Collective


## Input Parameters

- ***ls -*** the `TaoLineSearch` context
- ***func -*** the objective and gradient evaluation routine
- ***ctx -*** the (optional) user-defined context for private data



## Calling sequence of `func`
```none
PetscErrorCode func(TaoLinesearch ls, Vec x, PetscReal *f, Vec g, void *ctx);
```

- ***ls -*** the linesearch object
- ***x -*** input vector
- ***f -*** function value
- ***g -*** gradient vector
- ***ctx (optional) user-*** defined context





## Note
Use this routine only if you want the line search objective and gradient
evaluation routines to be different from the `Tao`'s objective
and gradient evaluation routines.

Some algorithms (lcl, gpcg) set their own objective routine for the
line search, application programmers should be wary of overriding the
default objective routine.


## See Also
 [](ch_tao), `Tao`, `TaoLineSearch`, `TaoLineSearchCreate()`, `TaoLineSearchSetObjectiveRoutine()`, `TaoLineSearchSetGradientRoutine()`, `TaoLineSearchUseTaoRoutines()`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/tao/linesearch/interface/taolinesearch.c.html#TaoLineSearchSetObjectiveAndGradientRoutine">src/tao/linesearch/interface/taolinesearch.c</A>


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


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