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.. _mpi_comm_size:
MPI_Comm_size
=============
.. include_body
:ref:`MPI_Comm_size` |mdash| Returns the size of the group associated with a
communicator.
SYNTAX
------
C Syntax
^^^^^^^^
.. code-block:: c
#include <mpi.h>
int MPI_Comm_size(MPI_Comm comm, int *size)
Fortran Syntax
^^^^^^^^^^^^^^
.. code-block:: fortran
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_COMM_SIZE(COMM, SIZE, IERROR)
INTEGER COMM, SIZE, IERROR
Fortran 2008 Syntax
^^^^^^^^^^^^^^^^^^^
.. code-block:: fortran
USE mpi_f08
MPI_Comm_size(comm, size, ierror)
TYPE(MPI_Comm), INTENT(IN) :: comm
INTEGER, INTENT(OUT) :: size
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
INPUT PARAMETER
---------------
* ``comm``: Communicator (handle).
OUTPUT PARAMETERS
-----------------
* ``size``: Number of processes in the group of comm (integer).
* ``ierror``: Fortran only: Error status (integer).
DESCRIPTION
-----------
This function indicates the number of processes involved in a
communicator. For MPI_COMM_WORLD, it indicates the total number of
processes available. This function is equivalent to accessing the
communicator's group with :ref:`MPI_Comm_group`, computing the size using
:ref:`MPI_Group_size`, and then freeing the temporary group via :ref:`MPI_Group_free`.
If the communicator is an inter-communicator (enables communication
between two groups), this function returns the size of the local group.
To return the size of the remote group, use the :ref:`MPI_Comm_remote_size`
function.
This call is often used with :ref:`MPI_Comm_rank` to determine the amount of
concurrency available for a specific library or program. :ref:`MPI_Comm_rank`
indicates the rank of the process that calls it in the range from 0 . .
. size-1, where size is the return value of :ref:`MPI_Comm_size`.
NOTE
----
MPI_COMM_NULL is not considered a valid argument to this function.
ERRORS
------
.. include:: ./ERRORS.rst
.. seealso::
* :ref:`MPI_Comm_group`
* :ref:`MPI_Comm_rank`
* :ref:`MPI_Comm_compare`
|
