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# MatZeroRowsStencil

Zeros all entries (except possibly the main diagonal) of a set of rows of a matrix indicated by a `MatStencil`. 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 indicated by an array of `MatStencil`

- 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

        MatStencil idxm(4, m)

and the values inserted using

        idxm(MatStencil_i, 1) = i
        idxm(MatStencil_j, 1) = j
        idxm(MatStencil_k, 1) = k
        idxm(MatStencil_c, 1) = c
       etc

## See Also

Matrices, `Mat`, `MatStencil`, `MatZeroRowsIS()`, `MatZeroRowsColumns()`, `MatZeroRowsLocalIS()`, `MatZeroRows()`, `MatZeroEntries()`, `MatZeroRowsLocal()`, `MatSetOption()`, `MatZeroRowsColumnsLocal()`, `MatZeroRowsColumnsLocalIS()`, `MatZeroRowsColumnsIS()`, `MatZeroRowsColumnsStencil()`

## Level

intermediate

## Location

src/mat/interface/matrix.c

Index of all Mat routines
Table of Contents for all manual pages
Index of all manual pages