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# KSPBCGSLSetXRes
Sets the parameter governing when exact residuals will be used instead of computed residuals. 
## Synopsis
```
#include "petscksp.h" 
PetscErrorCode KSPBCGSLSetXRes(KSP ksp, PetscReal delta)
```
Logically Collective


## Input Parameters

- ***ksp -*** iterative context of type `KSPBCGSL`
- ***delta -*** computed residuals are used alone when delta is not positive



## Options Database Key

- ***-ksp_bcgsl_xres delta -*** Threshold used to decide when to refresh computed residuals





## See Also
 [](ch_ksp), `KSPBCGSLSetEll()`, `KSPBCGSLSetPol()`, `KSP`, `KSPCBGSL`, `KSPBCGSLSetUsePseudoinverse()`

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/impls/bcgsl/bcgsl.c.html#KSPBCGSLSetXRes">src/ksp/ksp/impls/bcgsl/bcgsl.c</A>


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


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