MPI_Intercomm_create(3) Open MPI MPI_Intercomm_create(3)
NAME
MPI_Intercomm_create - Creates an intercommunicator from two intracom-
municators.
SYNTAX
C Syntax
#include <mpi.h>
int MPI_Intercomm_create(MPI_Comm local_comm, int local_leader,
MPI_Comm peer_comm, int remote_leader, int tag, MPI_Comm *newintercomm)
Fortran Syntax
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_INTERCOMM_CREATE(LOCAL_COMM, LOCAL_LEADER, PEER_COMM,
REMOTE_LEADER, TAG, NEWINTERCOMM, IERROR)
INTEGER LOCAL_COMM, LOCAL_LEADER, PEER_COMM, REMOTE_LEADER
INTEGER TAG, NEWINTERCOMM, IERROR
Fortran 2008 Syntax
USE mpi_f08
MPI_Intercomm_create(local_comm, local_leader, peer_comm, remote_leader,
tag, newintercomm, ierror)
TYPE(MPI_Comm), INTENT(IN) :: local_comm, peer_comm
INTEGER, INTENT(IN) :: local_leader, remote_leader, tag
TYPE(MPI_Comm), INTENT(OUT) :: newintercomm
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
C++ Syntax
#include <mpi.h>
Intercomm Intracomm::Create_intercomm(int local_leader, const
Comm& peer_comm, int remote_leader, int tag) const
INPUT PARAMETERS
local_comm
The communicator containing the process that initiates the
inter-communication (handle).
local_leader
Rank of local group leader in local_comm (integer).
peer_comm "Peer" communicator; significant only at the local_leader
(handle).
remote_leader
Rank of remote group leader in peer_comm; significant only at
the local_leader (integer).
tag Message tag used to identify new intercommunicator (integer).
OUTPUT PARAMETERS
newintercomm
Created intercommunicator (handle).
IERROR Fortran only: Error status (integer).
DESCRIPTION
This call creates an intercommunicator. It is collective over the union
of the local and remote groups. Processes should provide identical lo-
cal_comm and local_leader arguments within each group. Wildcards are
not permitted for remote_leader, local_leader, and tag.
This call uses point-to-point communication with communicator
peer_comm, and with tag tag between the leaders. Thus, care must be
taken that there be no pending communication on peer_comm that could
interfere with this communication.
If multiple MPI_Intercomm_creates are being made, they should use dif-
ferent tags (more precisely, they should ensure that the local and re-
mote leaders are using different tags for each MPI_intercomm_create).
NOTES
We recommend using a dedicated peer communicator, such as a duplicate
of MPI_COMM_WORLD, to avoid trouble with peer communicators.
The MPI 1.1 Standard contains two mutually exclusive comments on the
input intracommunicators. One says that their respective 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 in-
tercommunicators (like MPI_Intercomm_merge ) do not make sense if the
groups are not disjoint.
ERRORS
Almost all MPI routines return an error value; C routines as the value
of the function and Fortran routines in the last argument. C++ func-
tions do not return errors. If the default error handler is set to
MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
will be used to throw an MPI::Exception object.
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for
I/O function errors. The error handler may be changed with
MPI_Comm_set_errhandler; 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.
SEE ALSO
MPI_Intercomm_merge
MPI_Comm_free
MPI_Comm_remote_group
MPI_Comm_remote_size
4.1.2 Nov 24, 2021 MPI_Intercomm_create(3)
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