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MPI_Intercomm_create.3.rst

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MPI_Intercomm_create

:ref:`MPI_Intercomm_create` |mdash| Creates an intercommunicator from two intracommunicators.

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

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 local_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 different tags (more precisely, they should ensure that the local and remote 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 intercommunicators (like :ref:`MPI_Intercomm_merge` ) do not make sense if the groups are not disjoint.

ERRORS

.. seealso::
   * :ref:`MPI_Intercomm_merge`
   * :ref:`MPI_Comm_free`
   * :ref:`MPI_Comm_remote_group`
   * :ref:`MPI_Comm_remote_size`