I can't run mpirun np X Cobaya-run input.yaml with Polychord

[vivianmiranda]

I can't run mpirun np X Cobaya-run input.yaml with Polychord

[JesusTorrado]

Hi Vivian,

As you say, it looks like PolyChord is not talking to Python's MPI properly (even though Python's MPI itself is working). Most likely, the proper MPI libraries were not loaded at the time PolyChord was compiled.

I suggest the following diagnosis and possible fix:

0. Perform the MPI test at https://cobaya.readthedocs.io/en/latest/installation.html (this is important to check that Python's MPI has been loaded at this moment).
1. Go to the PolyChord installation folder under [your_modules]/code/PolyChord and re-compile it: make veryclean; make; python setup.py install --user (omit the --user flag if using Anaconda).
2. Clear the chains folder with rm -rf chains/*, run python run_PyPolyChord.py and check that it does not fail.
3. Repeat the last step, now with mpirun -n [X>1].

Did it work? If it did, would you try to run your case again? Otherwise, let me know.

[JesusTorrado]

After a second look, I am more inclined to think that this is a race condition, so if the 1st solution does not work (please, check it out anyway), try the following: substitute the 1st 4 lines of code in the run_polychord function in PolyChord/PyPolychord/__init__.py with

    try:
        from mpi4py import MPI
        comm = MPI.COMM_WORLD
        rank = comm.Get_rank()
    except ImportError:
        rank = 0

    if not os.path.exists(settings.base_dir) and rank == 0:
        os.makedirs(settings.base_dir)

    if not os.path.exists(settings.cluster_dir) and rank == 0:
        os.makedirs(settings.cluster_dir)

I am going to submit an issue to the official PolyChord repo.

[vivianmiranda]

It is indeed a race condition...your change of code fixed!