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.. _mpi_cart_sub:
MPI_Cart_sub
============
.. include_body
:ref:`MPI_Cart_sub` |mdash| Partitions a communicator into subgroups, which form
lower-dimensional Cartesian subgrids.
SYNTAX
------
C Syntax
^^^^^^^^
.. code-block:: C
#include <mpi.h>
int MPI_Cart_sub(MPI_Comm comm, const int remain_dims[], MPI_Comm *comm_new)
Fortran Syntax
^^^^^^^^^^^^^^
.. code-block:: Fortran
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
^^^^^^^^^^^^^^^^^^^
.. code-block:: Fortran
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
.. code-block:: c
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
------
.. include:: ./ERRORS.rst
.. seealso::
* :ref:`MPI_Cart_create`
|
