# TaoAppSetHessianSolveRoutine

Sets the routine that solves a linear system involving the Hessian operator, (or approximate Hessian).

## Synopsis

    #include "tao.h"
    int TaoAppSetHessianSolveRoutine(TAO_APPLICATION taoapp, int (*ah)(TAO_APPLICATION,Vec,Vec,PetscTruth*,void*),void *ctx)

Collective on TAO_APPLICATION

## Input Parameters

| taoapp | - the TAO_APPLICATION context
| ah | - gradient evaluation routine
| ctx | - [optional] user-defined function context

## Calling sequence of func

        ah (TAO_APPLICATION taoapp,Vec vin,Vec vout, PetscTruth* success, void *ctx);

| taoapp | - the TAO_APPLICATION context
| v | - input vector
| ctx | - user-defined function gradient context set from TaoAppSetGradientRoutine()

## Note

This routine is to be used only with the LMVM and BLMVM solvers. These solvers do not use Hessian information, but can incorporate very approximate Hessian information into the routine.

## Keywords

TAO_APPLICATION, set, hessian

## See Also

TaoAppSetHessianRoutine()

Level:intermediate
Location:src/petsctao/application/petscapp/tao_app_fg.c
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