NAME

       MPI_Comm_compare -  Compares two communicators

SYNOPSIS

       int MPI_Comm_compare(MPI_Comm comm1, MPI_Comm comm2, int *result)

INPUT PARAMETERS

       comm1  - comm1 (handle)
       comm2  - comm2 (handle)

OUTPUT PARAMETERS

       result - integer which is MPI_IDENT if the contexts and groups are the same, MPI_CONGRUENT
              if different contexts but identical groups, MPI_SIMILAR if different  contexts  but
              similar groups, and MPI_UNEQUAL otherwise

USING 'MPI_COMM_NULL' WITH 'MPI_COMM_COMPARE'

       It  is  an  error  to use MPI_COMM_NULL as one of the arguments to MPI_Comm_compare .  The
       relevant sections of the MPI standard are

       .  (2.4.1 Opaque Objects) A null handle argument is an erroneous IN argument in MPI calls,
       unless an exception is explicitly stated in the text that defines the function.

       .   (5.4.1.  Communicator Accessors) where there is no text in MPI_COMM_COMPARE allowing a
       null handle.

THREAD AND INTERRUPT SAFETY

       This routine is thread-safe.  This means that this routine may be safely used by  multiple
       threads  without the need for any user-provided thread locks.  However, the routine is not
       interrupt safe.  Typically, this is due to the use of memory allocation routines  such  as
       malloc  or  other  non-MPICH runtime routines that are themselves not interrupt-safe.  (To
       perform the communicator comparisions, this routine may  need  to  allocate  some  memory.
       Memory allocation is not interrupt-safe, and hence this routine is only thread-safe.)

NOTES FOR FORTRAN

       All  MPI  routines  in  Fortran  (except  for MPI_WTIME and MPI_WTICK ) have an additional
       argument ierr at the end of the argument list.  ierr  is  an  integer  and  has  the  same
       meaning  as  the  return  value  of  the  routine  in  C.   In  Fortran,  MPI routines are
       subroutines, and are invoked with the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran.

ERRORS

       All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error value;  C  routines  as
       the  value of the function and Fortran routines in the last argument.  Before the value is
       returned, the current MPI error handler is called.  By default, this error handler  aborts
       the  MPI  job.   The  error  handler  may  be  changed  with  MPI_Comm_set_errhandler (for
       communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler  (for  RMA
       windows).   The  MPI-1  routine  MPI_Errhandler_set may be used but its use is deprecated.
       The predefined error handler MPI_ERRORS_RETURN may be used to cause  error  values  to  be
       returned.   Note  that  MPI  does  not  guarentee that an MPI program can continue past an
       error; however, MPI implementations will attempt to continue whenever possible.

       MPI_SUCCESS
              - No error; MPI routine completed successfully.
       MPI_ERR_ARG
              - Invalid argument.  Some argument is invalid and is not identified by  a  specific
              error class (e.g., MPI_ERR_RANK ).

                                            11/12/2016                        MPI_Comm_compare(3)