# ISAllGather

Given an index set (IS) on each processor, generates a large index set (same on each processor) by concatenating together each processors index set.

### Synopsis

    #include "petscsys.h"
    #include "petscis.h"
    PetscErrorCode PETSCVEC_DLLEXPORT ISAllGather(IS is,IS *isout)

Collective on IS

### Input Parameter

is -the distributed index set

### Output Parameter

isout -the concatenated index set (same on all processors)

### Notes

ISAllGather() is clearly not scalable for large index sets.

The IS created on each processor must be created with a common communicator (e.g., PETSC_COMM_WORLD). If the index sets were created with PETSC_COMM_SELF, this routine will not work as expected, since each process will generate its own new IS that consists only of itself.

### See Also

ISCreateGeneral(), ISCreateStride(), ISCreateBlock(), ISAllGatherIndices()

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

### Examples

src/ksp/examples/tutorials/ex10.c.html