.. _mpi_comm_rank:


MPI_Comm_rank
=============

.. include_body

:ref:`MPI_Comm_rank` |mdash| Determines the rank of the calling process in the
communicator.


SYNTAX
------


C Syntax
^^^^^^^^

.. code-block:: c

   #include <mpi.h>

   int MPI_Comm_rank(MPI_Comm comm, int *rank)


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

.. code-block:: fortran

   USE MPI
   ! or the older form: INCLUDE 'mpif.h'
   MPI_COMM_RANK(COMM, RANK, IERROR)
   	INTEGER	COMM, RANK, IERROR


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

.. code-block:: fortran

   USE mpi_f08
   MPI_Comm_rank(comm, rank, ierror)
   	TYPE(MPI_Comm), INTENT(IN) :: comm
   	INTEGER, INTENT(OUT) :: rank
   	INTEGER, OPTIONAL, INTENT(OUT) :: ierror


INPUT PARAMETERS
----------------
* ``comm``: Communicator (handle).

OUTPUT PARAMETERS
-----------------
* ``rank``: Rank of the calling process in group of comm (integer).
* ``ierror``: Fortran only: Error status (integer).

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

This function gives the rank of the process in the particular
communicator's group. It is equivalent to accessing the communicator's
group with :ref:`MPI_Comm_group`, computing the rank using :ref:`MPI_Group_rank`, and
then freeing the temporary group via :ref:`MPI_Group_free`.

Many programs will be written with the manager-worker model, where one
process (such as the rank-zero process) will play a supervisory role,
and the other processes will serve as compute nodes. In this framework,
:ref:`MPI_Comm_size` and :ref:`MPI_Comm_rank` are useful for determining the roles of
the various processes of a communicator.


ERRORS
------

.. include:: ./ERRORS.rst

.. seealso::
   * :ref:`MPI_Comm_group`
   * :ref:`MPI_Comm_size`
   * :ref:`MPI_Comm_compare`