dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Sep 01, 2011 at 01:49:13PM +0200, Harish Narayanan wrote:
> On 9/1/11 1:43 PM, Harish Narayanan wrote:
> > On 2/17/10 3:44 PM, Anders Logg wrote:
> >> It is now possible to specify the direction of interior facets such
> >> that one may know which side of a facet is ('+') and which side is
> >> ('-').
> >>
> >> To use this, attach a MeshFunction over the facets that specifies for
> >> each facet which cell (by the cell index) that is the first ('+') side
> >> of the cell:
> >>
> >>   MeshFunction<uint>* facet_orientation = mesh.data().create_mesh_function("facet orientation");
> >>
> >> Then just fill in the appropriate values in facet_orientation.
> >>
> >> This is useful for integration over facets where the two sides are not
> >> treated symmetrically, for example using upwinding or in multiphysics
> >> problems with an interior boundary cutting through the mesh.
> >
> > I am trying to use this (from Python) and it is not clear to me how this
> > works.
> >
> > I do:
> >
> > orientation = mesh.data().mesh_function("facet orientation")
> > # Populate the mesh function orientation
> >
> > How is this information used in the assembler?
>
> No matter, it works with "facet_orientation" instead.

Yes. It is used by the assembler to pick the first of the two cells
forming the macro elements surrounding interior facets.

Check in Assembler.cpp and search for "facet_orientation" and then
check the function adjacent_cells() in Facet.cpp.

--
Anders