:orphan:
# PCGALERKIN
Build (part of) a preconditioner by P S R (where P is often R^T) 


## Note
Use
```none
     `PCGalerkinSetRestriction`(pc,R) and/or `PCGalerkinSetInterpolation`(pc,P)
     `PCGalerkinGetKSP`(pc,&ksp);
     `KSPSetOperators`(ksp,A,....)
     ...
```



## Developer Notes
If `KSPSetOperators()` has not been called on the inner `KSP` then `PCGALERKIN` could use `MatRARt()` or `MatPtAP()` to compute
the operators automatically.

Should there be a prefix for the inner `KSP`?

There is no `KSPSetFromOptions_Galerkin()` that calls `KSPSetFromOptions()` on the inner `KSP`


## See Also
 `PCCreate()`, `PCSetType()`, `PCType`, `PC`,
`PCSHELL`, `PCKSP`, `PCGalerkinSetRestriction()`, `PCGalerkinSetInterpolation()`, `PCGalerkinGetKSP()`

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/galerkin/galerkin.c.html#PCGALERKIN">src/ksp/pc/impls/galerkin/galerkin.c</A>


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


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