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# KSPMonitorTrueResidual
Prints the true residual norm, as well as the (possibly preconditioned) approximate residual norm, at each iteration of an iterative solver. 
## Synopsis
```
#include "petscksp.h" 
PetscErrorCode KSPMonitorTrueResidual(KSP ksp, PetscInt n, PetscReal rnorm, PetscViewerAndFormat *vf)
```
Collective


## Input Parameters

- ***ksp   -*** iterative context
- ***n     -*** iteration number
- ***rnorm -*** 2-norm (preconditioned) residual value (may be estimated).
- ***vf    -*** The viewer context



## Options Database Key

- ***-ksp_monitor_true_residual -*** Activates `KSPMonitorTrueResidual()`





## Notes
When using right preconditioning, these values are equivalent.

This is not called directly by users, rather one calls `KSPMonitorSet()`, with this function as an argument, to cause the monitor
to be used during the `KSP` solve.


## See Also
 [](ch_ksp), `KSP`, `KSPMonitorSet()`, `KSPMonitorResidual()`, `KSPMonitorTrueResidualMaxNorm()`, `PetscViewerAndFormat`

## Level
intermediate

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


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


[Index of all KSP routines](index.md)  
[Table of Contents for all manual pages](/manualpages/index.md)  
[Index of all manual pages](/manualpages/singleindex.md)