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

       INCLUDE 'mpif.h'
       MPI_COMM_TEST_INTER(COMM, FLAG, IERROR)
            INTEGER   COMM, IERROR
            LOGICAL   FLAG

C++ Syntax

       #include <mpi.h>
       bool Comm::Is_inter() const

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