.. _mpi_comm_split_type:


MPI_Comm_split_type
===================

.. include_body

:ref:`MPI_Comm_split_type` - Creates new communicators based on colors and
keys.


SYNTAX
------


C Syntax
^^^^^^^^

.. code-block:: c

   #include <mpi.h>

   int MPI_Comm_split_type(MPI_Comm comm, int split_type, int key,
   	MPI_Info info, MPI_Comm *newcomm)


Fortran Syntax
^^^^^^^^^^^^^^

.. code-block:: fortran

   USE MPI
   ! or the older form: INCLUDE 'mpif.h'
   MPI_COMM_SPLIT_TYPE(COMM, SPLIT_TYPE, KEY, INFO, NEWCOMM, IERROR)
   	INTEGER	COMM, SPLIT_TYPE, KEY, INFO, NEWCOMM, IERROR


Fortran 2008 Syntax
^^^^^^^^^^^^^^^^^^^

.. code-block:: fortran

   USE mpi_f08
   MPI_Comm_split_type(comm, split_type, key, info, newcomm, ierror)
   	TYPE(MPI_Comm), INTENT(IN) :: comm
   	INTEGER, INTENT(IN) :: split_type, key
   	TYPE(MPI_Info), INTENT(IN) :: info
   	TYPE(MPI_Comm), INTENT(OUT) :: newcomm
   	INTEGER, OPTIONAL, INTENT(OUT) :: ierror


INPUT PARAMETERS
----------------
* ``comm``: Communicator (handle).
* ``split_type``: Type of processes to be grouped together (integer).
* ``key``: Control of rank assignment (integer).
* ``info``: Info argument (handle).

OUTPUT PARAMETERS
-----------------
* ``newcomm``: New communicator (handle).
* ``ierror``: Fortran only: Error status (integer).

DESCRIPTION
-----------

This function partitions the group associated with *comm* into disjoint
subgroups, based on the type specified by *split_type*. Each subgroup
contains all processes of the same type. Within each subgroup, the
processes are ranked in the order defined by the value of the argument
*key*, with ties broken according to their rank in the old group. A new
communicator is created for each subgroup and returned in newcomm. This
is a collective call; all processes must provide the same *split_type*,
but each process is permitted to provide different values for key. An
exception to this rule is that a process may supply the type value
MPI_UNDEFINED, in which case newcomm returns MPI_COMM_NULL.


SPLIT TYPES
-----------

MPI_COMM_TYPE_SHARED
   This type splits the communicator into subcommunicators, each of
   which can create a shared memory region.

OMPI_COMM_TYPE_NODE
   Synonym for MPI_COMM_TYPE_SHARED.

OMPI_COMM_TYPE_HWTHREAD
   This type splits the communicator into subcommunicators, each of
   which belongs to the same hardware thread.

OMPI_COMM_TYPE_CORE
   This type splits the communicator into subcommunicators, each of
   which belongs to the same core/processing unit.

OMPI_COMM_TYPE_L1CACHE
   This type splits the communicator into subcommunicators, each of
   which belongs to the same L1 cache.

OMPI_COMM_TYPE_L2CACHE
   This type splits the communicator into subcommunicators, each of
   which belongs to the same L2 cache.

OMPI_COMM_TYPE_L3CACHE
   This type splits the communicator into subcommunicators, each of
   which belongs to the same L3 cache.

OMPI_COMM_TYPE_SOCKET
   This type splits the communicator into subcommunicators, each of
   which belongs to the same socket.

OMPI_COMM_TYPE_NUMA
   This type splits the communicator into subcommunicators, each of
   which belongs to the same NUMA-node.

OMPI_COMM_TYPE_BOARD
   This type splits the communicator into subcommunicators, each of
   which belongs to the same board.

OMPI_COMM_TYPE_HOST
   This type splits the communicator into subcommunicators, each of
   which belongs to the same host.

OMPI_COMM_TYPE_CU
   This type splits the communicator into subcommunicators, each of
   which belongs to the same computational unit.

OMPI_COMM_TYPE_CLUSTER
   This type splits the communicator into subcommunicators, each of
   which belongs to the same cluster.


NOTES
-----

The communicator keys denoted with an *OMPI\_* prefix instead of an
*MPI\_* prefix are specific to Open MPI, and are not part of the MPI
standard. Their use should be protected by the *OPEN_MPI* C preprocessor
macro.


ERRORS
------

.. include:: ./ERRORS.rst

.. seealso::
   * :ref:`MPI_Comm_create`
   * :ref:`MPI_Intercomm_create`
   * :ref:`MPI_Comm_dup`
   * :ref:`MPI_Comm_free`
   * :ref:`MPI_Comm_split`
