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 ).

                                                   11/12/2019                                MPI_Comm_compare(3)