# MatFactorSetSchurIS
Set indices corresponding to the Schur complement you wish to have computed 
## Synopsis
```
#include "petscmat.h" 
PetscErrorCode MatFactorSetSchurIS(Mat mat, IS is)
```
Collective


## Input Parameters

- ***mat -*** the factored matrix
- ***is -*** the index set defining the Schur indices (0-based)





## Notes
Call `MatFactorSolveSchurComplement()` or `MatFactorSolveSchurComplementTranspose()` after this call to solve a Schur complement system.

You can call `MatFactorGetSchurComplement()` or `MatFactorCreateSchurComplement()` after this call.

This functionality is only supported for `MATSOLVERMUMPS` and `MATSOLVERMKL_PARDISO`


## See Also
 `Mat`, `MatGetFactor()`, `MatFactorGetSchurComplement()`, `MatFactorRestoreSchurComplement()`, `MatFactorCreateSchurComplement()`, `MatFactorSolveSchurComplement()`,
`MatFactorSolveSchurComplementTranspose()`, `MatFactorSolveSchurComplement()`, `MATSOLVERMUMPS`, `MATSOLVERMKL_PARDISO`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/interface/matrix.c.html#MatFactorSetSchurIS">src/mat/interface/matrix.c</A>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/mpi/mumps/mumps.c.html#MatFactorSetSchurIS_MUMPS">MatFactorSetSchurIS_MUMPS in src/mat/impls/aij/mpi/mumps/mumps.c</A><BR>


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


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