# MatSubMatrixVirtualUpdate
Updates a `MATSUBMATRIX` virtual submatrix 
## Synopsis
```
#include "petscmat.h" 
PetscErrorCode MatSubMatrixVirtualUpdate(Mat N, Mat A, IS isrow, IS iscol)
```
Collective on N


## Input Parameters

- ***N -*** submatrix to update
- ***A -*** full matrix in the submatrix
- ***isrow -*** rows in the update (same as the first time the submatrix was created)
- ***iscol -*** columns in the update (same as the first time the submatrix was created)





## Note
Most will use `MatCreateSubMatrix()` which provides a more efficient representation if it is available.


## See Also
 MATSUBMATRIX`, `MatCreateSubMatrixVirtual()`

## Level
developer

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/submat/submat.c.html#MatSubMatrixVirtualUpdate">src/mat/impls/submat/submat.c</A>


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


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