:orphan:
# TaoGetHessian
Gets the function to compute the Hessian as well as the location to store the matrix. 
## Synopsis
```
#include "petsctao.h" 
PetscErrorCode TaoGetHessian(Tao tao, Mat *H, Mat *Hpre, PetscErrorCode (**func)(Tao, Vec, Mat, Mat, void *), void **ctx)
```
Not Collective


## Input Parameter

- ***tao  -*** the `Tao` context



## OutputParameters

- ***H    -*** Matrix used for the hessian
- ***Hpre -*** Matrix that will be used to construct the preconditioner, can be the same as `H`
- ***func -*** Hessian evaluation routine
- ***ctx  -*** user-defined context for private data for the Hessian evaluation routine



## Calling sequence of `func`
```none
PetscErrorCode func(Tao tao, Vec x, Mat H, Mat Hpre, void *ctx);
```

- ***tao  -*** the Tao  context
- ***x    -*** input vector
- ***H    -*** Hessian matrix
- ***Hpre -*** matrix used to construct the preconditioner, usually the same as `H`
- ***ctx  -*** [optional] user-defined Hessian context





## See Also
 [](ch_tao), `Tao`, TaoType`, `TaoGetObjective()`, `TaoGetGradient()`, `TaoGetObjectiveAndGradient()`, `TaoSetHessian()`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/tao/interface/taosolver_hj.c.html#TaoGetHessian">src/tao/interface/taosolver_hj.c</A>


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


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