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MPI_Comm_rank.3.rst

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MPI_Comm_rank

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

SYNTAX

C Syntax

#include <mpi.h>

int MPI_Comm_rank(MPI_Comm comm, int *rank)

Fortran Syntax

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

Fortran 2008 Syntax

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

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