ffc team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Wed, Aug 31, 2005 at 05:57:50PM +0200, jhoffman@xxxxxxxxxxx wrote:
> > I'm planning to add a list of predefined operators and operands to FFC
> > to simplify and beautify the notation anyway, so this would fit well
> > into that category.
> >
> > Operators that will be added include grad(), rot() and div().
> >
> > Operands that will be added include h (mesh size) and d (space dimension).
> >
> > Any other suggestions?
> 
> I find it useful to be able use some more geometry information (in
> particular when we start integrating on surfaces):
> 
> vol - volume of cell
> area(i) - area for local face i
> hface(i) - h for local face i
> ...
> same for local edges?

I can understand if you need h (mesh size) and v (volume), but do you
really need area of a specific local face?

> It may also be useful to be able to identify a local face from a
> collection of vertices; that is, while visiting a cell in the assembly one
> might want to get information about the local faces.

I think all this messy stuff should be hidden. We need to do this when
we implement integrals over boundaries, but everything that needs to
be visible in FFC is the new operator

    *ds

Karin Kraft and Johan Jansson have already implemented a prototype
version of boundary integrals in DOLFIN as far as I understand, so I
only need to implement the remaining portions in FFC. I will probably
also need to request some new features from FIAT so I can tabulate
basis functions on faces/edges of the reference cells.

> On the other hand, we may avoid a lot of this since we intend to assemble
> separately over faces (and edges), and then vol and h may be reduced to
> the corresponding functions for the face when looping over the faces.

Do you need both vol and h at the same time in the stabilization?

/Anders