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MPI_Intercomm_merge(3)                MPI               MPI_Intercomm_merge(3)


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

       comm   - 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 PARAMETER

       comm_out
              - 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


LOCATION

       src/mpi/comm/intercomm_merge.c

                                   9/20/2012            MPI_Intercomm_merge(3)

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