# 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

## 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

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 donâ€™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


Matrices, Mat, MatZeroRowsIS(), MatZeroRowsColumns(), MatZeroRowsLocalIS(), MatZeroRowsStencil(), MatZeroEntries(), MatZeroRowsLocal(), MatSetOption(), MatZeroRowsColumnsLocal(), MatZeroRowsColumnsLocalIS(), MatZeroRowsColumnsIS(), MatZeroRows()