Hi, Does MPI_COMM_WORLD exist in any sense before MPI_Init is called? In particular, does this code violate the standard? InitializeMyApp(MPI_Comm comm, int argc, char **argv) { int initialized; MPI_Initialized(&initialized); if (!initialized) MPI_Init(&argc, &argv); /* call some function that uses comm */ } int main(int argc, char **argv) { MPI_Comm comm = MPI_COMM_WORLD; InitializeMyApp(comm, argc, argv); : } My instinct is that this is wrong, but I would like to be sure before I complain about it. It appears to work with some existing implementations, but it looks sketchy to me. Bruce