MPI_Comm_test_inter(3)

NAME
MPI_Comm_test_inter - Tests to see if a comm is an intercommunicator.

SYNTAX

C Syntax
#include <mpi.h>
int MPI_Comm_test_inter(MPI_Comm comm, int *flag)

Fortran Syntax
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_COMM_TEST_INTER(COMM, FLAG, IERROR)
	INTEGER	COMM, IERROR
	LOGICAL	FLAG

Fortran 2008 Syntax
USE mpi_f08
MPI_Comm_test_inter(comm, flag, ierror)
	TYPE(MPI_Comm), INTENT(IN) :: comm
	LOGICAL, INTENT(OUT) :: flag
	INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETER

comm
    Communicator (handle).

OUTPUT PARAMETERS

flag     (Logical.)

IERROR
    Fortran only: Error status (integer).

DESCRIPTION
This local routine allows the calling process to determine the type of a communicator. It returns true for an intercommunicator, false for an intracommunicator.

The type of communicator also affects the value returned by three other functions. When dealing with an intracommunicator (enables communication within a single group), the functions listed below return the expected values, group size, group, and rank. When dealing with an inter-communicator, however, they return the following values:

MPI_Comm_size	Returns the size of the local group.
MPI_Comm_group	Returns the local group.
MPI_Comm_rank	Returns the rank in the local group.

To return the remote group and remote group size of an inter-communicator, use the MPI_Comm_remote_group and MPI_Comm_remote_size functions.

The operation MPI_Comm_compare is valid for intercommunicators. Both communicators must be either intra- or intercommunicators, or else MPI_UNEQUAL results. Both corresponding local and remote groups must compare correctly to get the results MPI_CONGRUENT and MPI_SIMILAR. In particular, it is possible for MPI_SIMILAR to result because either the local or remote groups were similar but not identical.

The following accessors provide consistent access to the remote group of an intercommunicator: MPI_Comm_remote_size, MPI_Comm_remote_group.

The intercommunicator accessors (MPI_Comm_test_inter, MPI_Comm_remote_size, MPI_Comm_remote_group) are all local operations.

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_remote_group
MPI_Comm_remote_size
MPI_Intercomm_create
MPI_Intercomm_merge