.. _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
------

Almost all MPI routines return an error value; C routines as the value
of the function and Fortran routines in the last argument.

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
:ref:`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.


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