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MPI_Comm_test_inter

:ref:`MPI_Comm_test_inter` |mdash| 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:

:ref:`MPI_Comm_size`
Returns the size of the local group.
:ref:`MPI_Comm_group`
Returns the local group.
:ref:`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 :ref:`MPI_Comm_remote_group` and :ref:`MPI_Comm_remote_size` functions.

The operation :ref:`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: :ref:`MPI_Comm_remote_size`, :ref:`MPI_Comm_remote_group`.

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

ERRORS

.. seealso::
   * :ref:`MPI_Comm_remote_group`
   * :ref:`MPI_Comm_remote_size`
   * :ref:`MPI_Intercomm_create`
   * :ref:`MPI_Intercomm_merge`