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# KSPCGSetRadius
Sets the radius of the trust region 
## Synopsis
```
#include "petscksp.h" 
PetscErrorCode KSPCGSetRadius(KSP ksp, PetscReal radius)
```
Logically Collective


## Input Parameters

- ***ksp    -*** the iterative context
- ***radius -*** the trust region radius (0 is the default that disable the use of the radius)





## Note
When radius is greater then 0, the Steihaugh-Toint trick is used


## See Also
 [](ch_ksp), `KSP`, `KSPCG`, `KSPNASH`, `KSPSTCG`, `KSPGLTR`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/impls/cg/cgtype.c.html#KSPCGSetRadius">src/ksp/ksp/impls/cg/cgtype.c</A>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/impls/cg/cg.c.html#KSPCGSetRadius_CG">KSPCGSetRadius_CG in src/ksp/ksp/impls/cg/cg.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/impls/cg/gltr/gltr.c.html#KSPCGSetRadius_GLTR">KSPCGSetRadius_GLTR in src/ksp/ksp/impls/cg/gltr/gltr.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/impls/cg/nash/nash.c.html#KSPCGSetRadius_NASH">KSPCGSetRadius_NASH in src/ksp/ksp/impls/cg/nash/nash.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/impls/cg/stcg/stcg.c.html#KSPCGSetRadius_STCG">KSPCGSetRadius_STCG in src/ksp/ksp/impls/cg/stcg/stcg.c</A><BR>


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


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