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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.