# MatSchurComplementUpdateSubMatrices
Updates the Schur complement matrix object with new submatrices 
## Synopsis
```
#include "petscksp.h" 
PetscErrorCode MatSchurComplementUpdateSubMatrices(Mat S, Mat A00, Mat Ap00, Mat A01, Mat A10, Mat A11)
```
Collective on S


## Input Parameters

- ***S                -*** matrix obtained with `MatCreateSchurComplement()` (or `MatSchurSetSubMatrices()`) and implementing the action of A11 - A10 ksp(A00,Ap00) A01
- ***A00,A01,A10,A11  -*** the four parts of A = [A00 A01; A10 A11] (A11 is optional)
- ***Ap00             -*** preconditioning matrix for use in ksp(A00,Ap00) to approximate the action of A^{-1}.





## Notes
All four matrices must have the same MPI communicator

A00 and  A11 must be square matrices

All of the matrices provided must have the same sizes as was used with `MatCreateSchurComplement()` or `MatSchurComplementSetSubMatrices()`
though they need not be the same matrices.

This can only be called after `MatCreateSchurComplement()` or `MatSchurComplementSetSubMatrices()`, it cannot be called immediately after `MatSetType`(S,`MATSCHURCOMPLEMENT`);


## Developer Note
This code is almost identical to `MatSchurComplementSetSubMatrices()`. The API should be refactored.


## See Also
 [](chapter_ksp), `Mat`, `MatCreateNormal()`, `MatMult()`, `MatCreate()`, `MatSchurComplementGetKSP()`, `MatCreateSchurComplement()`

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/utils/schurm/schurm.c.html#MatSchurComplementUpdateSubMatrices">src/ksp/ksp/utils/schurm/schurm.c</A>


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


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