MatGetValues#

Gets a block of local values from a matrix.

Synopsis#

#include "petscmat.h" 
PetscErrorCode MatGetValues(Mat mat, PetscInt m, const PetscInt idxm[], PetscInt n, const PetscInt idxn[], PetscScalar v[])

Not Collective; can only return values that are owned by the give process

Input Parameters#

mat - the matrix
v - a logically two-dimensional array for storing the values
m - the number of rows
idxm - the global indices of the rows
n - the number of columns
idxn - the global indices of the columns

Notes#

The user must allocate space (m*n PetscScalars) for the values, v. The values, v, are then returned in a row-oriented format, analogous to that used by default in MatSetValues().

MatGetValues() uses 0-based row and column numbers in Fortran as well as in C.

MatGetValues() requires that the matrix has been assembled with MatAssemblyBegin()/MatAssemblyEnd(). Thus, calls to MatSetValues() and MatGetValues() CANNOT be made in succession without intermediate matrix assembly.

Negative row or column indices will be ignored and those locations in v will be left unchanged.

For the standard row-based matrix formats, idxm can only contain rows owned by the requesting MPI rank. That is, rows with global index greater than or equal to rstart and less than rend where rstart and rend are obtainable from MatGetOwnershipRange(mat,&rstart,&rend).