The Great and Terrible implementation of MPI-2

function index


Maps process to Cartesian topology information
int MPI_Cart_map(
  MPI_Comm comm_old,
  int ndims,
  int *dims,
  int *periods,
  int *newrank


[in] input communicator (handle)
[in] number of dimensions of Cartesian structure (integer)
[in] integer array of size ndims specifying the number of processes in each coordinate direction
[in] logical array of size ndims specifying the periodicity specification in each coordinate direction
[out] reordered rank of the calling process; MPI_UNDEFINED if calling process does not belong to grid (integer)


MPI_CART_MAP computes an "optimal" placement for the calling process on the physical machine.  In general this function will not be called by the user directly, unless he or she is creating additional virtual topology capability other than that provided by MPI.

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 communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).
Invalid dimension argument. A dimension argument is null or its length is less than or equal to zero.
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_map.

#include "mpi.h"
#include <stdio.h>

int main( int argc, char *argv[] )
int errs = 0;
int dims[2];
int periods[2];
int size, rank, newrank;

    MPI_Init( &argc, &argv );
    MPI_Comm_size( MPI_COMM_WORLD, &size );
    MPI_Comm_rank( MPI_COMM_WORLD, &rank );

/* This defines a cartision grid with a single point */
    periods[0] = 1;
    dims[0] = 1;
    MPI_Cart_map( MPI_COMM_WORLD, 1, dims, periods, &newrank );
if (rank > 0) {
if (newrank != MPI_UNDEFINED) {
            printf( "rank outside of input communicator not UNDEFINED\n" );fflush(stdout);
    else {
if (rank != newrank) {
            printf( "Newrank not defined and should be 0\n" );fflush(stdout);
return 0;