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# PCGALERKIN

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

## Note

Use

         `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

KSP: Linear System Solvers, `PCCreate()`, `PCSetType()`, `PCType`, `PC`, `PCSHELL`, `PCKSP`, `PCGalerkinSetRestriction()`, `PCGalerkinSetInterpolation()`, `PCGalerkinGetKSP()`

## Level

intermediate

## Location

src/ksp/pc/impls/galerkin/galerkin.c

Index of all PC routines
Table of Contents for all manual pages
Index of all manual pages