SYNTAX

   C Syntax
          #include <mpi.h>

          int MPI_Dims_create(int nnodes, int ndims, int dims[])

   Fortran Syntax
          USE MPI
          ! or the older form: INCLUDE 'mpif.h'
          MPI_DIMS_CREATE(NNODES, NDIMS, DIMS, IERROR)
               INTEGER NNODES, NDIMS, DIMS(*), IERROR

   Fortran 2008 Syntax
          USE mpi_f08
          MPI_Dims_create(nnodes, ndims, dims, ierror)
               INTEGER, INTENT(IN) :: nnodes, ndims
               INTEGER, INTENT(INOUT) :: dims(ndims)
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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 return result of the function and
       Fortran routines in the last argument.

       Before the error value is returned, the current MPI  error  handler  associated  with  the  communication
       object  (e.g.,  communicator, window, file) is called.  If no communication object is associated with the
       MPI call, then the call is considered attached to MPI_COMM_SELF and will call the  associated  MPI  error
       handler.   When   MPI_COMM_SELF   is   not  initialized  (i.e.,  before  MPI_Init/MPI_Init_thread,  after
       MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial  error  handler.
       The  initial  error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using
       the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info  key  to  MPI_Comm_spawn/‐
       MPI_Comm_spawn_multiple.   If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
       error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is  called  for  all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When
         called  on  a  communicator,  it  acts  as if MPI_Abort was called on that communicator. If called on a
         window or file, acts as if MPI_Abort was called on a communicator containing the group of processes  in
         the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler then MPI_Comm_set_errhandler

       • MPI_File_create_errhandler then MPI_File_set_errhandler

       • MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

       • MPI_Win_create_errhandler then MPI_Win_set_errhandler

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page for a full list of MPI error codes.

       See the Error Handling section of the MPI-3.1 standard for more information.

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                                MPI_DIMS_CREATE(3)