The Great and Terrible implementation of MPI-2

function index


Determines process rank in communicator given Cartesian location
int MPI_Cart_rank(
  MPI_Comm comm,
  int *coords,
  int *rank


[in] communicator with cartesian structure (handle)
[in] integer array (of size ndims, the number of dimensions of the Cartesian topology associated with comm) specifying the cartesian coordinates of a process
[out] rank of specified process (integer)


For a process group with cartesian structure, the function MPI_CART_RANK translates the logical process coordinates to process ranks as they are used by the point-to-point routines.

For dimension i with periods(i) = true, if the coordinate, coords(i), is out of range, that is, coords(i) < 0 or coords(i) dims(i), it is shifted back to the interval
0 coords(i) < dims(i) automatically.

Out-of-range coordinates are erroneous for non-periodic dimensions. Versions of MPICH before 1.2.2 returned MPI_PROC_NULL for the rank in this case.

Thread and Interrupt Safety

This routine is both thread- and interrupt-safe. This means that this routine may safely be used by multiple threads and from within a signal handler.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.


All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

No error; MPI routine completed successfully.
Invalid topology. Either there is no topology associated with this communicator, or it is not the correct type (e.g., MPI_CART when expecting MPI_GRAPH).
Invalid source or destination rank. Ranks must be between zero and the size of the communicator minus one; ranks in a receive (MPI_Recv, MPI_Irecv, MPI_Sendrecv, etc.) may also be MPI_ANY_SOURCE.
Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).

Example Code

The following sample code illustrates MPI_Cart_rank.

/* A two-dimensional torus of 12 processes in a 4x3 grid */
int main(int argc, char *argv[])
    int rank, size;
    MPI_Comm comm;
    int dim[2], period[2], reorder;
    int coord[2], id;

    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    if (size != 12)
        printf("Please run with 12 processes.\n");fflush(stdout);
        MPI_Abort(MPI_COMM_WORLD, 1);

    dim[0]=4; dim[1]=3;
    period[0]=1; period[1]=0;
    MPI_Cart_create(MPI_COMM_WORLD, 2, dim, period, reorder, &comm);
    if (rank == 5)
        MPI_Cart_coords(comm, rank, 2, coord);
        printf("Rank %d coordinates are %d %d\n", rank, coord[0], coord[1]);fflush(stdout);
        coord[0]=3; coord[1]=1;
        MPI_Cart_rank(comm, coord, &id);
        printf("The processor at position (%d, %d) has rank %d\n", coord[0], coord[1], id);fflush(stdout);
return 0;