MPI_Intercomm_create(3) LAM/MPI MPI_Intercomm_create(3)
MPI_Intercomm_create - Creates an intercommuncator from two intracommunicators
int MPI_Intercomm_create(MPI_Comm lcomm, int lleader,
MPI_Comm pcomm, int pleader, int tag,
lcomm - Local (intra)communicator
- Rank in local_comm of leader (often 0)
pcomm - Remote communicator
- Rank in peer_comm of remote leader (often 0)
tag - Message tag to use in constructing intercommunicator; if multiple MPI_Inter-
comm_creates are being made, they should use different tags (more precisely, ensure
that the local and remote leaders are using different tags for each MPI_inter-
- Created intercommunicator
The MPI 1.1 Standard contains two mutually exclusive comments on the input intracommunica-
tors. One says that their repective groups must be disjoint; the other that the leaders
can be the same process. After some discussion by the MPI Forum, it has been decided that
the groups must be disjoint. Note that the reason given for this in the standard is not
the reason for this choice; rather, the other operations on intercommunicators (like
MPI_Intercomm_merge ) do not make sense if the groups are not disjoint.
NOTES FOR FORTRAN
All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argu-
ment 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.
If an error occurs in an MPI function, the current MPI error handler is called to handle
it. By default, this error handler aborts the MPI job. The error handler may be changed
with MPI_Errhandler_set ; the predefined error handler MPI_ERRORS_RETURN may be used to
cause error values to be returned (in C and Fortran; this error handler is less useful in
with the C++ MPI bindings. The predefined error handler MPI::ERRORS_THROW_EXCEPTIONS
should be used in C++ if the error value needs to be recovered). Note that MPI does not
guarantee that an MPI program can continue past an error.
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. The C++ bindings for
MPI do not return error values; instead, error values are communicated by throwing excep-
tions of type MPI::Exception (but not by default). Exceptions are only thrown if the
error value is not MPI::SUCCESS
Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI functions will return
upon an error, there will be no way to recover what the actual error value was.
- 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 ).
- Invalid tag argument. Tags must be non-negative; tags in a receive ( MPI_Recv ,
MPI_Irecv , MPI_Sendrecv , etc.) may also be MPI_ANY_TAG
. The largest tag value is available through the the attribute MPI_TAG_UB
- Invalid argument. Some argument is invalid and is not identified by a specific
error class. This is typically a NULL pointer or other such error.
- This error is returned when some part of the LAM/MPI implementation is unable to
- Invalid source or destination rank. Ranks must be between zero and the size of
the communicator minus one; ranks in a receive ( MPI_Recv , MPI_Irecv ,
MPI_Sendrecv , etc.) may also be MPI_ANY_SOURCE
MPI_Intercomm_merge, MPI_Comm_free, MPI_Comm_remote_group,
For more information, please see the official MPI Forum web site, which contains the text
of both the MPI-1 and MPI-2 standards. These documents contain detailed information about
each MPI function (most of which is not duplicated in these man pages).
The LAM Team would like the thank the MPICH Team for the handy program to generate man
pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz ), the initial for-
matting, and some initial text for most of the MPI-1 man pages.
LAM/MPI 6.5.8 11/10/2002 MPI_Intercomm_create(3)