petsc-3.3-p7 2013-05-11

ISSum

Computes the sum (union) of two index sets.

#include "petscis.h"  
PetscErrorCode  ISSum(IS is1,IS is2,IS *is3)

Only sequential version (at the moment)

	is1	- index set to be extended
	is2	- index values to be added

is3 -the sum; this can not be is1 or is2

If n1 and n2 are the sizes of the sets, this takes O(n1+n2) time;

Both index sets need to be sorted on input.