I am attempting to convert an existing application to use the new MPI_Neighbor_* routines for halo updates. The trouble I'm having is that the application fixes the ranks in a right-handed cartesian grid while that produced by MPI_Cart_create appears to be left-handed. MPI_Cart_create produces a rank ordering for a 4x4 grid 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 The application expects the ranks to be ordered like 12 13 14 15 8 9 10 11 4 5 6 7 0 1 2 3 I've read the MPI-3 manual at http://www.mpi-forum.org/docs/mpi-3.0/mpi30-report.pdf What am I missing? Can I manipulate the rank placement produced by MPI_Cart_create to suite this application? Daniel Kokron NASA Ames (ARC-TN) SciCon group 301-286-3959