.. _mpi_group_difference:

MPI_Group_difference
====================

.. include_body

:ref:`MPI_Group_difference` |mdash| Makes a group from the difference of two groups.

SYNTAX
------

C Syntax
^^^^^^^^

.. code-block:: c

   #include <mpi.h>

   int MPI_Group_difference(MPI_Group group1, MPI_Group group2,
       MPI_Group *newgroup)

Fortran Syntax
^^^^^^^^^^^^^^

.. code-block:: fortran

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

   MPI_GROUP_DIFFERENCE(GROUP1, GROUP2, NEWGROUP, IERROR)
       INTEGER GROUP1, GROUP2, NEWGROUP, IERROR

Fortran 2008 Syntax
^^^^^^^^^^^^^^^^^^^

.. code-block:: fortran

   USE mpi_f08

   MPI_Group_difference(group1, group2, newgroup, ierror)
       TYPE(MPI_Group), INTENT(IN) :: group1, group2
       TYPE(MPI_Group), INTENT(OUT) :: newgroup
       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS
----------------

* ``group1`` : First group (handle).
* ``group2`` : Second group (handle).

OUTPUT PARAMETERS
-----------------

* ``newgroup`` : Difference group (handle).
* ``ierror`` : Fortran only: Error status (integer).

DESCRIPTION
-----------

The set-like operations are defined as follows:

* union |mdash| All elements of the first group (group1), followed by all
   elements of second group (group2) that are not in the first group
* intersect |mdash| all elements of the first group that are also in the
   second group, ordered as in first group
* difference |mdash| 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
------

.. include:: ./ERRORS.rst

.. seealso:: :ref:`MPI_Group_free`
