# KSPSetMonitor

Sets an ADDITIONAL function to be called at every iteration to monitor the residual/error etc.

### Synopsis

    #include "petscksp.h"
    PetscErrorCode PETSCKSP_DLLEXPORT KSPSetMonitor(KSP ksp,PetscErrorCode (*monitor)(KSP,PetscInt,PetscReal,void*),void *mctx,PetscErrorCode (*monitordestroy)(void*))

Collective on KSP

### Input Parameters

| ksp | - iterative context obtained from KSPCreate()
| monitor | - pointer to function (if this is PETSC_NULL, it turns off monitoring
| mctx | - [optional] context for private data for the monitor routine (use PETSC_NULL if no context is desired)
| monitordestroy | - [optional] routine that frees monitor context (may be PETSC_NULL)

### Calling Sequence of monitor

        monitor (KSP ksp, int it, PetscReal rnorm, void *mctx)

| ksp | - iterative context obtained from KSPCreate()
| it | - iteration number
| rnorm | - (estimated) 2-norm of (preconditioned) residual
| mctx | - optional monitoring context, as set by KSPSetMonitor()

### Options Database Keys

| -ksp_monitor | - sets KSPDefaultMonitor()
| -ksp_truemonitor | - sets KSPTrueMonitor()
| -ksp_xmonitor | - sets line graph monitor, uses KSPLGMonitorCreate()
| -ksp_xtruemonitor | - sets line graph monitor, uses KSPLGMonitorCreate()
| -ksp_singmonitor | - sets KSPSingularValueMonitor()
| -ksp_cancelmonitors | - cancels all monitors that have been hardwired into a code by calls to KSPSetMonitor(), but does not cancel those set via the options database.

### Notes

The default is to do nothing. To print the residual, or preconditioned residual if KSPSetNormType(ksp,KSP_PRECONDITIONED_NORM) was called, use KSPDefaultMonitor() as the monitoring routine, with a null monitoring context.

Several different monitoring routines may be set by calling KSPSetMonitor() multiple times; all will be called in the order in which they were set.

### Keywords

KSP, set, monitor

### See Also

KSPDefaultMonitor(), KSPLGMonitorCreate(), KSPClearMonitor()

Level:beginner
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/examples/tutorials/ex9.c.html
src/ksp/examples/tutorials/ex2f.F.html
src/snes/examples/tutorials/ex30.c.html