# MatZeroRowsColumnsStencil
Zeros all row and column entries (except possibly the main diagonal) of a set of rows and columns of a matrix. 
## Synopsis
```
#include "petscmat.h" 
PetscErrorCode MatZeroRowsColumnsStencil(Mat mat, PetscInt numRows, const MatStencil rows[], PetscScalar diag, Vec x, Vec b)
```
Collective on mat


## Input Parameters

- ***mat -*** the matrix
- ***numRows -*** the number of rows/columns to remove
- ***rows -*** the grid coordinates (and component number when dof > 1) for matrix rows
- ***diag -*** value put in all diagonals of eliminated rows (0.0 will even eliminate diagonal entry)
- ***x -*** optional vector of solutions for zeroed rows (other entries in vector are not used)
- ***b -*** optional vector of right hand side, that will be adjusted by provided solution



## Notes
See `MatZeroRowsColumns()` for details on how this routine operates.

The grid coordinates are across the entire grid, not just the local portion

In Fortran idxm and idxn should be declared as
```none
MatStencil idxm(4,m)
```
and the values inserted using
```none
idxm(MatStencil_i,1) = i
```
```none
idxm(MatStencil_j,1) = j
```
```none
idxm(MatStencil_k,1) = k
```
```none
idxm(MatStencil_c,1) = c
```
etc

For periodic boundary conditions use negative indices for values to the left (below 0; that are to be
obtained by wrapping values from right edge). For values to the right of the last entry using that index plus one
etc to obtain values that obtained by wrapping the values from the left edge. This does not work for anything but the
`DM_BOUNDARY_PERIODIC` boundary type.

For indices that don't mean anything for your case (like the k index when working in 2d) or the c index when you have
a single value per point) you can skip filling those indices.




## See Also
 `MatZeroRowsIS()`, `MatZeroRowsColumns()`, `MatZeroRowsLocalIS()`, `MatZeroRowsStencil()`, `MatZeroEntries()`, `MatZeroRowsLocal()`, `MatSetOption()`,
`MatZeroRowsColumnsLocal()`, `MatZeroRowsColumnsLocalIS()`, `MatZeroRowsColumnsIS()`, `MatZeroRows()`

## Level
intermediate

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

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex35.c.html">src/snes/tutorials/ex35.c.html</A><BR>


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


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