# KSPSetConvergenceTest

Sets the function to be used to determine convergence.

### Synopsis

    #include "petscksp.h"
    PetscErrorCode PETSCKSP_DLLEXPORT KSPSetConvergenceTest(KSP ksp,PetscErrorCode (*converge)(KSP,PetscInt,PetscReal,KSPConvergedReason*,void*),void *cctx)

Collective on KSP

### Input Parameters

| ksp | - iterative context obtained from KSPCreate()
| converge | - pointer to int function
| cctx | - context for private data for the convergence routine (may be null)

### Calling sequence of converge

        converge (KSP ksp, int 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()

### 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, KSPDefaultConverged(), 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.

### Keywords

KSP, set, convergence, test, context

### See Also

KSPDefaultConverged(), KSPGetConvergenceContext()

Level:advanced
Location:src/ksp/ksp/interface/itfunc.c
Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages

### Examples

src/ksp/ksp/examples/tutorials/ex2f.F.html