petsc-3.8.4 2018-03-24

DMDAGetElements

Gets an array containing the indices (in local coordinates) of all the local elements

#include "petscdmda.h"   
PetscErrorCode  DMDAGetElements(DM dm,PetscInt *nel,PetscInt *nen,const PetscInt *e[])

Not Collective

dm -the DM object

	nel	- number of local elements
	nen	- number of element nodes
	e	- the local indices of the elements' vertices

Call DMDARestoreElements() once you have finished accessing the elements.

Each process uniquely owns a subset of the elements. That is no element is owned by two or more processes.

If on each process you integrate over its owned elements and use ADD_VALUES in Vec/MatSetValuesLocal() then you'll obtain the correct result.