The low-level function for general graph topologies as in
the Cartesian topologies given in Section 
is as follows. This call is collective.
MPI_UNDEFINED
MPI_Graph_map(MPI_Comm comm, int nnodes, int *index, int *edges, int *newrank)
MPI_GRAPH_MAP(COMM, NNODES, INDEX, EDGES, NEWRANK, IERROR)INTEGER COMM, NNODES, INDEX(*), EDGES(*), NEWRANK, IERROR
