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MPI_Comm_create_group.3.rst

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MPI_Comm_create_group

:ref:`MPI_Comm_create_group` - Creates a new communicator.

SYNTAX

C Syntax

#include <mpi.h>

int MPI_Comm_create_group(MPI_Comm comm, MPI_Group group, int tag, MPI_Comm *newcomm)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_COMM_CREATE_GROUP(COMM, GROUP, TAG, NEWCOMM, IERROR)
    INTEGER COMM, GROUP, TAG, NEWCOMM, IERROR

Fortran 2008 Syntax

USE mpi_f08

MPI_Comm_create_group(comm, group, tag, newcomm, ierror)
    TYPE(MPI_Comm), INTENT(IN) :: comm
    TYPE(MPI_Group), INTENT(IN) :: group
    INTEGER, INTENT(IN) :: tag
    TYPE(MPI_Comm), INTENT(OUT) :: newcomm
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

  • comm : Communicator (handle).
  • group : Group, which is a subset of the group of comm (handle).
  • tag : Tag (integer).

OUTPUT PARAMETERS

  • newcomm : New communicator (handle).
  • ierror : Fortran only: Error status (integer).

DESCRIPTION

:ref:`MPI_Comm_create_group` is similar to :ref:`MPI_Comm_create`; however, :ref:`MPI_Comm_create` must be called by all processes in the group of comm, whereas :ref:`MPI_Comm_create_group` must be called by all processes in group, which is a subgroup of the group of comm. In addition, :ref:`MPI_Comm_create_group` requires that comm is an intracommunicator. :ref:`MPI_Comm_create_group` returns a new intracommunicator, newcomm, for which the group argument defines the communication group. No cached information propagates from comm to newcomm. Each process must provide a group argument that is a subgroup of the group associated with comm; this could be MPI_GROUP_EMPTY. If a non-empty group is specified, then all processes in that group must call the function, and each of these processes must provide the same arguments, including a group that contains the same members with the same ordering. Otherwise the call is erroneous. If the calling process is a member of the group given as the group argument, then newcomm is a communicator with group as its associated group. If the calling process is not a member of group, e.g., group is MPI_GROUP_EMPTY, then the call is a local operation and MPI_COMM_NULL is returned as newcomm.

NOTES

:ref:`MPI_Comm_create_group` provides a means of making a subset of processes for the purpose of separate MIMD computation, with separate communication space. newcomm, which is created by :ref:`MPI_Comm_create_group`, can be used in subsequent calls to :ref:`MPI_Comm_create_group` (or other communicator constructors) to further subdivide a computation into parallel sub-computations. A more general service is provided by :ref:`MPI_Comm_split`.

ERRORS

.. seealso::
   * :ref:`MPI_Comm_create`