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MPI_Cart_sub.3.rst

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MPI_Cart_sub

:ref:`MPI_Cart_sub` |mdash| Partitions a communicator into subgroups, which form lower-dimensional Cartesian subgrids.

SYNTAX

C Syntax

#include <mpi.h>

int MPI_Cart_sub(MPI_Comm comm, const int remain_dims[], MPI_Comm *comm_new)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_CART_SUB(COMM, REMAIN_DIMS, COMM_NEW, IERROR)
    INTEGER COMM, COMM_NEW, IERROR
    LOGICAL REMAIN_DIMS(*)

Fortran 2008 Syntax

USE mpi_f08

MPI_Cart_sub(comm, remain_dims, newcomm, ierror)
    TYPE(MPI_Comm), INTENT(IN) :: comm
    LOGICAL, INTENT(IN) :: remain_dims(*)
    TYPE(MPI_Comm), INTENT(OUT) :: newcomm
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

  • comm : Communicator with Cartesian structure (handle).
  • remain_dims : The ith entry of remain_dims specifies whether the ith
    dimension is kept in the subgrid (true) or is dropped (false) (logical vector).

OUTPUT PARAMETERS

  • comm_new : Communicator containing the subgrid that includes the
    calling process (handle).
  • ierror : Fortran only: Error status (integer).

DESCRIPTION

If a Cartesian topology has been created with :ref:`MPI_Cart_create`, the function :ref:`MPI_Cart_sub` can be used to partition the communicator group into subgroups that form lower-dimensional Cartesian subgrids, and to build for each subgroup a communicator with the associated subgrid Cartesian topology. (This function is closely related to :ref:`MPI_Comm_split`.)

Example: Assume that MPI_Cart_create( ..., comm) has defined a (2 x 3 x 4) grid. Let remain_dims = (true, false, true). Then a call to

MPI_Cart_sub(comm, remain_dims, comm_new);

will create three communicators, each with eight processes in a 2 x 4 Cartesian topology. If remain_dims = (false, false, true) then the call to MPI_Cart_sub(comm, remain_dims, comm_new) will create six nonoverlapping communicators, each with four processes, in a one-dimensional Cartesian topology.

ERRORS

.. seealso::
   * :ref:`MPI_Cart_create`