#include "petscis.h" PetscErrorCode ISEqual(IS is1,IS is2,PetscBool *flg)Collective on IS
| is1, is2 | - The index sets being compared | 
| flg | - output flag, either PETSC_TRUE (if both index sets have the same indices), or PETSC_FALSE if the index sets differ by size or by the set of indices) | 
Each processor has to have the same indices in the two sets, for example,
          Processor
            0      1
   is1 = {0, 1} {2, 3}
   is2 = {2, 3} {0, 1}
will return false.