Pass custom mpi4py communicator

[adematti]

Hi,
Thanks for this sampler!
Here are two suggestions:

• it'd be nice to be able to provide, through the Python wrapper, the proper mpi4py communicator in case it is not COMM_WORLD (e.g. to have several runs in parallel).
• it may be worth avoiding MPI_ANY_TAG, e.g. in

  PolyChordLite/src/polychord/mpi_utils.F90

  Line 492 in e00386b

  MPI_ANY_TAG, &!

  , which may conflict with potential MPI communication between e.g. the user-provided logposterior and dumper.

I have a branch that addresses the above suggestions I think, here: https://github.com/adematti/PolyChordLite/tree/mpi4py
(I can file a PR if desired)
Best

[williamjameshandley]

Hi @adematti. Both of these sound like a great idea. Feel free to file a PR.