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

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

4.1.2                                             Nov 24, 2021                            MPI_Comm_test_inter(3)