17.2.69. MPI_Comm_rank

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

! or the older form: INCLUDE 'mpif.h'
     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

  • 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.

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.