# ISSum

Computes the sum (union) of two index sets.

### Synopsis

    #include "petscis.h"
    int ISSum(IS is1,IS is2,IS *isout)

Collective on IS

### Input Parameter

| is1 | - first index set
| is2 | - index values to be added

### Output Parameters

isout -is1 + is2 The index set is2 is appended to is1 removing duplicates

### Notes

Negative values are removed from the lists. This requires O(imax-imin) memory and O(imax-imin) work, where imin and imax are the bounds on the indices in is1 and is2.

### See Also

ISDestroy(), ISView(), ISDifference()

Level:intermediate
Location: src/vec/is/utils/isdiff.c
Index of all IS routines
Table of Contents for all manual pages
Index of all manual pages