:orphan:
# KSPSetConvergenceTest
Sets the function to be used to determine convergence. 
## Synopsis
```
#include "petscksp.h" 
#include "petscmat.h" 
PetscErrorCode KSPSetConvergenceTest(KSP ksp, PetscErrorCode (*converge)(KSP, PetscInt, PetscReal, KSPConvergedReason *, void *), void *cctx, PetscErrorCode (*destroy)(void *))
```
Logically Collective


## Input Parameters

- ***ksp -*** iterative context obtained from `KSPCreate()`
- ***converge -*** pointer to the function
- ***cctx    -*** context for private data for the convergence routine (may be null)
- ***destroy -*** a routine for destroying the context (may be null)



## Calling sequence of `converge`
```none
PetscErrorCode converge(KSP ksp, PetscInt it, PetscReal rnorm, KSPConvergedReason *reason, void *mctx)
```

- ***ksp -*** iterative context obtained from `KSPCreate()`
- ***it -*** iteration number
- ***rnorm -*** (estimated) 2-norm of (preconditioned) residual
- ***reason -*** the reason why it has converged or diverged
- ***cctx  -*** optional convergence context, as set by `KSPSetConvergenceTest()`



## Calling Sequence of `destroy`
```none
PetscErrorCode destroy(void *cctx)
```




## Notes
Must be called after the `KSP` type has been set so put this after
a call to `KSPSetType()`, or `KSPSetFromOptions()`.

The default convergence test, `KSPConvergedDefault()`, aborts if the
residual grows to more than 10000 times the initial residual.

The default is a combination of relative and absolute tolerances.
The residual value that is tested may be an approximation; routines
that need exact values should compute them.

In the default PETSc convergence test, the precise values of reason
are macros such as `KSP_CONVERGED_RTOL`, which are defined in petscksp.h.


## See Also
 [](ch_ksp), `KSP`, `KSPConvergedDefault()`, `KSPGetConvergenceContext()`, `KSPSetTolerances()`, `KSP`, `KSPGetConvergenceTest()`, `KSPGetAndClearConvergenceTest()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/interface/itfunc.c.html#KSPSetConvergenceTest">src/ksp/ksp/interface/itfunc.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex2f.F90.html">src/ksp/ksp/tutorials/ex2f.F90</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex57f.F90.html">src/ksp/ksp/tutorials/ex57f.F90</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex71.c.html">src/ksp/ksp/tutorials/ex71.c</A><BR>


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


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