NAME

       MPI_Intercomm_merge -  Creates an intracommuncator from an intercommunicator

SYNOPSIS

       int MPI_Intercomm_merge(MPI_Comm intercomm, int high, MPI_Comm *newintracomm)

INPUT PARAMETERS

       intercomm
              - Intercommunicator (handle)
       high   -   Used  to  order  the  groups  within  comm  (logical)  when  creating  the  new
              communicator.  This is a boolean value; the group  that  sets  high  true  has  its
              processes  ordered after the group that sets this value to false.  If all processes
              in the intercommunicator provide the same value,  the  choice  of  which  group  is
              ordered first is arbitrary.

OUTPUT PARAMETERS

       newintracomm
              - Created intracommunicator (handle)

NOTES

       While  all  processes may provide the same value for the high parameter, this requires the
       MPI implementation to determine which group of processes should be ranked first.

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.

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.

ALGORITHM

       \neAllocate contexts \neLocal and remote group leaders swap high values  \neDetermine  the
       high value.  \neMerge the two groups and make the intra-communicator

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_COMM
              -  Invalid  communicator.   A  common error is to use a null communicator in a call
              (not even allowed in MPI_Comm_rank ).
       MPI_ERR_INTERN
              - This error is returned when some part of the MPICH implementation  is  unable  to
              acquire memory.

SEE ALSO

       MPI_Intercomm_create, MPI_Comm_free

                                            11/12/2016                     MPI_Intercomm_merge(3)