petsc-3.8.4 2018-03-24

MatZeroRowsLocal

Zeros all entries (except possibly the main diagonal) of a set of rows of a matrix; using local numbering of rows.

Synopsis

#include "petscmat.h" 
PetscErrorCode MatZeroRowsLocal(Mat mat,PetscInt numRows,const PetscInt rows[],PetscScalar diag,Vec x,Vec b)

Collective on Mat

Input Parameters

	mat	- the matrix
	numRows	- the number of rows to remove
	rows	- the global row indices
	diag	- value put in all diagonals of eliminated rows
	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

Before calling MatZeroRowsLocal(), the user must first set the local-to-global mapping by calling MatSetLocalToGlobalMapping().

For the AIJ matrix formats this removes the old nonzero structure, but does not release memory. For the dense and block diagonal formats this does not alter the nonzero structure.

If the option MatSetOption(mat,MAT_KEEP_NONZERO_PATTERN,PETSC_TRUE) the nonzero structure of the matrix is not changed (even for AIJ and BAIJ matrices) the values are merely zeroed.

The user can set a value in the diagonal entry (or for the AIJ and row formats can optionally remove the main diagonal entry from the nonzero structure as well, by passing 0.0 as the final argument).

You can call MatSetOption(mat,MAT_NO_OFF_PROC_ZERO_ROWS,PETSC_TRUE) if each process indicates only rows it owns that are to be zeroed. This saves a global synchronization in the implementation.

MatZeroRowsLocal

Synopsis

Input Parameters

Notes

See Also