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.