osx man page for mpi_comm_rank

MPI_Comm_rank(3OpenMPI) 												   MPI_Comm_rank(3OpenMPI)

NAME
       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
       INCLUDE 'mpif.h'
       MPI_COMM_RANK(COMM, RANK, IERROR)
	    INTEGER   COMM, RANK, IERROR

C++ Syntax
       #include <mpi.h>
       int Comm::Get_rank() const

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 MPI_Comm_group, computing the rank using MPI_Group_rank, and then freeing the temporary group via MPI_Group_free.

       Many programs will be written with the master-slave 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, MPI_Comm_size and MPI_Comm_rank are useful for determining the
       roles of the various processes of a communicator.

ERRORS
       Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ func-
       tions  do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI:Exception object.

       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 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.

SEE ALSO
       MPI_Comm_group
       MPI_Comm_size
       MPI_Comm_compare

Open MPI 1.2							  September 2006					   MPI_Comm_rank(3OpenMPI)