:ref:`MPI_Comm_create_group` |mdash| Creates a new communicator.
#include <mpi.h>
int MPI_Comm_create_group(MPI_Comm comm, MPI_Group group, int tag, MPI_Comm *newcomm)
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_COMM_CREATE_GROUP(COMM, GROUP, TAG, NEWCOMM, IERROR)
INTEGER COMM, GROUP, TAG, NEWCOMM, IERROR
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
comm
: Communicator (handle).group
: Group, which is a subset of the group of comm (handle).tag
: Tag (integer).
newcomm
: New communicator (handle).ierror
: Fortran only: Error status (integer).
: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.
: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`.
.. seealso::
* :ref:`MPI_Comm_create`