Determining MPI Rank from Environment Variable.md

Tags: #mpi

Debugging and profiling MPI applications occasionally needs to identify which MPI rank is executing from the environment (e.g. from within a shell script). This is MPI distribution dependent - see the environment variables below.

OpenMPI

OMPI_COMM_WORLD_RANK holds the rank index and OMPI_COMM_WORLD_SIZE holds the world size.

Intel MPI

PMI_RANK holds the rank index and PMI_SIZE holds the world size.