NAME

       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

       MPI_Comm_create_group  is  similar  to  MPI_Comm_create;  however, MPI_Comm_create must be
       called by all processes in the group of comm, whereas MPI_Comm_create_group must be called
       by  all  processes  in  group,  which  is  a  subgroup  of the group of comm. In addition,
       MPI_Comm_create_group requires that comm is  an  intracommunicator.  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

       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
       MPI_Comm_create_group,  can be used in subsequent calls to MPI_Comm_create_group (or other
       communicator  constructors)  to  further  subdivide  a  computation  into  parallel   sub-
       computations. A more general service is provided by MPI_Comm_split.

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and
       Fortran routines in the last argument.

       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_Comm_create