MPI_Comm_split with MPI_UNDEFINED as color would produce a subcommunicator == MPI_COMM_NULL.
currently, mxx::comm.split(color) when supplied with MPI_UNDEFINED does not appear to handle this case properly. Subsequent calls (even when logic is branched with "if (color == x)") results in an MPI error/exception.
MPI_Comm_split with MPI_UNDEFINED as color would produce a subcommunicator == MPI_COMM_NULL.
currently, mxx::comm.split(color) when supplied with MPI_UNDEFINED does not appear to handle this case properly. Subsequent calls (even when logic is branched with "if (color == x)") results in an MPI error/exception.