MPI_Comm_rank(3)

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
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 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++ functions 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