MPI_Dims_create(3)                 Open MPI                 MPI_Dims_create(3)



NAME
       MPI_Dims_create  - Creates a division of processors in a Cartesian
       grid.


SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Dims_create(int nnodes, int ndims, int *dims)


Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_DIMS_CREATE(NNODES, NDIMS, DIMS, IERROR)
            INTEGER   NNODES, NDIMS, DIMS(*), IERROR


C++ Syntax
       #include <mpi.h>
       void Compute_dims(int nnodes, int ndims, int dims[])


INPUT PARAMETERS
       nnodes    Number of nodes in a grid (integer).

       ndims     Number of Cartesian dimensions (integer).


IN/OUT PARAMETER
       dims      Integer array of size ndims specifying the number of nodes in
                 each dimension.


OUTPUT PARAMETER
       IERROR    Fortran only: Error status (integer).


DESCRIPTION
       For Cartesian topologies, the function MPI_Dims_create helps the user
       select a balanced distribution of processes per coordinate direction,
       depending on the number of processes in the group to be balanced and
       optional constraints that can be specified by the user. One use is to
       partition all the processes (the size of MPI_COMM_WORLD's group) into
       an n-dimensional topology.

       The entries in the array dims are set to describe a Cartesian grid with
       ndims dimensions and a total of nnodes nodes. The dimensions are set to
       be as close to each other as possible, using an appropriate
       divisibility algorithm. The caller may further constrain the operation
       of this routine by specifying elements of array dims. If dims[i] is set
       to a positive number, the routine will not modify the number of nodes
       in dimension i; only those entries where  dims[i] = 0 are modified by
       the call.

       Negative input values of dims[i] are erroneous. An error will occur if
       nnodes is not a multiple of ((pi) over (i, dims[i] != 0)) dims[i].

       For dims[i] set by the call, dims[i] will be ordered in nonincreasing
       order. Array dims is suitable for use as input to routine
       MPI_Cart_create. MPI_Dims_create is local.

       Example:

       dims
       before                        dims
       call      function call       on return
       -----------------------------------------------------
       (0,0)     MPI_Dims_create(6, 2, dims)   (3,2)
       (0,0)     MPI_Dims_create(7, 2, dims)   (7,1)
       (0,3,0)   MPI_Dims_create(6, 3, dims)   (2,3,1)
       (0,3,0)   MPI_Dims_create(7, 3, dims)   erroneous call
       ------------------------------------------------------


ERRORS
       Almost all MPI routines return an error value; C routines as the value
       of the function and Fortran routines in the last argument. C++
       functions do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI:Exception object.

       Before the error value is returned, the current MPI error handler is
       called. By default, this error handler aborts the MPI job, except for
       I/O function errors. The error handler may be changed with
       MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN
       may be used to cause error values to be returned. Note that MPI does
       not guarantee that an MPI program can continue past an error.




1.4.1                            Jan 14, 2010               MPI_Dims_create(3)
