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

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 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,  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