NAME

       MPI_Group_union  - Produces a group by combining two groups.

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Group_union(MPI_Group group1, MPI_Group group2,
            MPI_Group *newgroup)

Fortran Syntax

       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_GROUP_UNION(GROUP1, GROUP2, NEWGROUP, IERROR)
            INTEGER   GROUP1, GROUP2, NEWGROUP, IERROR

Fortran 2008 Syntax

       USE mpi_f08
       MPI_Group_union(group1, group2, newgroup, ierror)
            TYPE(MPI_Group), INTENT(IN) :: group1, group2
            TYPE(MPI_Group), INTENT(OUT) :: newgroup
            INTEGER, OPTIONAL, INTENT(OUT) :: ierror

C++ Syntax

       #include <mpi.h>
       static Group Group::Union(const Group& group1, const Group& group2)

INPUT PARAMETERS

       group1    First group (handle).

       group2    Second group (handle).

OUTPUT PARAMETERS

       newgroup  Union group (handle).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       The set-like operations are defined as follows:

         o    union  --  All  elements  of  the first group (group1), followed by all elements of
              second group (group2) not in first.

         o    intersect -- all elements of the first group that are also  in  the  second  group,
              ordered as in first group.

         o    difference  --  all  elements  of the first group that are not in the second group,
              ordered as in the first group.

       Note that for these operations the order of processes in the output  group  is  determined
       primarily  by  order  in the first group (if possible) and then, if necessary, by order in
       the  second  group.  Neither  union  nor  intersection  are  commutative,  but  both   are
       associative.

       The new group can be empty, that is, equal to MPI_GROUP_EMPTY.

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and
       Fortran routines in the last argument. C++ functions do not return errors. If the  default
       error  handler  is  set  to  MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception
       mechanism will be used to throw an MPI::Exception object.

       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_Group_free