# KSPGuessSetTolerance
Sets the relative tolerance used in either eigenvalue (POD) or singular value (Fischer type 3) calculations. Ignored by the first and second Fischer types. 
## Synopsis
```
#include "petscksp.h"  
PetscErrorCode KSPGuessSetTolerance(KSPGuess guess, PetscReal tol)
```
Collective


## Input Parameter

- ***guess -*** `KSPGuess` object





## See Also
 [](chapter_ksp), `KSPGuess`, `KSPGuessType`, `KSPGuessSetFromOptions()`

## Level
developer

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

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/guess/impls/fischer/fischer.c.html#KSPGuessSetTolerance_Fischer">KSPGuessSetTolerance_Fischer in src/ksp/ksp/guess/impls/fischer/fischer.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/guess/impls/pod/pod.c.html#KSPGuessSetTolerance_POD">KSPGuessSetTolerance_POD in src/ksp/ksp/guess/impls/pod/pod.c</A><BR>


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


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