PETSc version 3.16.5
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# 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 on ksp

### 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

        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()

### 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

KSPConvergedDefault(), KSPGetConvergenceContext(), KSPSetTolerances(), KSP, KSPGetConvergenceTest(), KSPGetAndClearConvergenceTest()

### Level

advanced

### Location

src/ksp/ksp/interface/itfunc.c

### Examples

src/ksp/ksp/tutorials/ex71.c.html
src/ksp/ksp/tutorials/ex2f.F90.html
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