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MPI_Comm_test_inter

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

* MPI_Comm_remote_group * MPI_Comm_remote_size * MPI_Intercomm_create * MPI_Intercomm_merge