MatGetValuesLocal#

retrieves values from certain locations in a matrix using the local numbering of the indices defined previously by MatSetLocalToGlobalMapping()

Synopsis#

#include "petscmat.h" 
PetscErrorCode MatGetValuesLocal(Mat mat, PetscInt nrow, const PetscInt irow[], PetscInt ncol, const PetscInt icol[], PetscScalar y[])

Not Collective

Input Parameters#

mat - the matrix
nrow - number of rows
irow - the row local indices
ncol - number of columns
icol - the column local indices

Output Parameter#

y - a logically two-dimensional array of values

Notes#

If you create the matrix yourself (that is not with a call to DMCreateMatrix()) then you MUST call MatSetLocalToGlobalMapping() before using this routine.

This routine can only return values that are owned by the requesting MPI rank. That is, for standard matrix formats, rows that, in the global numbering, are greater than or equal to rstart and less than rend where rstart and rend are obtainable from MatGetOwnershipRange(mat,&rstart,&rend). One can determine if the resulting global row associated with the local row r is owned by the requesting MPI rank by applying the ISLocalToGlobalMapping set with MatSetLocalToGlobalMapping().

Developer Note#

This is labelled with C so does not automatically generate Fortran stubs and interfaces because it requires multiple Fortran interfaces depending on which arguments are scalar or arrays.