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MPI_Intercomm_merge(3) MPI MPI_Intercomm_merge(3)
MPI_Intercomm_merge - Creates an intracommuncator from an
int MPI_Intercomm_merge(MPI_Comm intercomm, int high, MPI_Comm *newintracomm)
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.
- Created intracommunicator (handle)
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-
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
\neAllocate contexts \neLocal and remote group leaders swap high values
\neDetermine the high value. \neMerge the two groups and make the
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.
- No error; MPI routine completed successfully.
- Invalid communicator. A common error is to use a null
communicator in a call (not even allowed in MPI_Comm_rank ).
- This error is returned when some part of the MPICH
implementation is unable to acquire memory.