Use of caching in redistribution

Redistribution With Caching

• Problem:
  In the earlier redistribution example a tag was passed to the redistribution routine to ensure safe message passing. For compatibility with MPI's collective communication routines we need to remove this tag but still guarantee safe message passing.
  In this example we show how to do this by caching a ``hidden'' communicator with the communicator passed into the redistribution routine.

  For compatibility with MPI collective communication routines we must also return an error code.