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# MatZeroRowsStencil
Zeros all entries (except possibly the main diagonal) of a set of rows of a matrix. These rows must be local to the process. 
## Synopsis
```
#include "petscmat.h" 
PetscErrorCode MatZeroRowsStencil(Mat mat, PetscInt numRows, const MatStencil rows[], PetscScalar diag, Vec x, Vec b)
```
Collective


## Input Parameters

- ***mat -*** the matrix
- ***numRows -*** the number of rows 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 `MatZeroRows()` for details on how this routine operates.

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

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.


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



## See Also
 [](ch_matrices), `Mat`, `MatZeroRowsIS()`, `MatZeroRowsColumns()`, `MatZeroRowsLocalIS()`, `MatZeroRowsl()`, `MatZeroEntries()`, `MatZeroRowsLocal()`, `MatSetOption()`,
`MatZeroRowsColumnsLocal()`, `MatZeroRowsColumnsLocalIS()`, `MatZeroRowsColumnsIS()`, `MatZeroRowsColumnsStencil()`

## Level
intermediate

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


---
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