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  
 inter-communicator (handle)


high  
 ordering of the local and remote groups in the new intra-communicator (logical)





Output Parameters




newintracomm  
 new intra-communicator (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


    

    

  1. Allocate contexts

  2. Local and remote group leaders swap high values

  3. Determine the high value.

  4. Merge 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 guarantee 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).





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_OTHER  
 Other error; use MPI_Error_string to get more information
about this error code. 





See Also

 MPI_Intercomm_create, MPI_Comm_free