PETSc version 3.17.4
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# ISExpand

Computes the union of two index sets, by concatenating 2 lists and removing duplicates.

### Synopsis

    #include "petscis.h"
    PetscErrorCode ISExpand(IS is1,IS is2,IS *isout)

Collective on IS

### Input Parameters

| 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.

The IS's do not need to be sorted.

### See Also

ISDestroy(), ISView(), ISDifference(), ISSum()

### Level

intermediate

### Location

src/vec/is/is/utils/isdiff.c

### Examples

src/ksp/ksp/tutorials/ex81.c.html
Index of all IS routines
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Index of all manual pages