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

       INCLUDE 'mpif.h'
       MPI_COMM_CREATE_GROUP(COMM, GROUP, TAG, NEWCOMM, IERROR)
            INTEGER   COMM, GROUP, TAG, NEWCOMM, 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