dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

On 01/12/10 23:07, Anders Logg wrote:
> On Wed, Dec 01, 2010 at 03:01:13PM -0800, Johan Hake wrote:
> > On Wednesday December 1 2010 14:52:32 Garth N. Wells wrote:
> > > On 01/12/10 22:25, Johan Hake wrote:
> > > > On Wednesday December 1 2010 14:06:59 Anders Logg wrote:
> > > > > On Wed, Dec 01, 2010 at 01:51:01PM -0800, Johan Hake wrote:
> > > > > > On Wednesday December 1 2010 11:19:28 noreply@xxxxxxxxxxxxx wrote:
> > > > > > > ------------------------------------------------------------
> > > > > > > revno: 5346
> > > > > > > committer: Garth N. Wells<gnw20@xxxxxxxxx>
> > > > > > > branch nick: dolfin-all
> > > > > > > timestamp: Wed 2010-12-01 19:15:42 +0000
> > > > > > >
> > > > > > > message:
> > > > > > >     Re-working of Function interfaces for removal of Data object.
> > > > > > >
> > > > > > >     Nearly all test running, but logic needs to be checked. Problem
> > > > > > >     remains
> > > > > > >
> > > > > > > with demos that use facet info.
> > > > > > >
> > > > > > >     Also need to sort out determning whether or nor a ufc::cell belongs
> > > > > > >     to a
> > > > > > >
> > > > > > > given mesh. modified:
> > > > > > There is a whole bunch of functionality that is lost with not having
> > > > > > access to a dolfin::Cell. Should this be added to ufc::cell?
> > > > >
> > > > > I assume we will keep all existing functionality in place, in
> > > > > particular the functions defined in SpecialFunctions.h.
> > > >
> > > > My point is that in the data argument you could access a dolfin::Cell.
> > > > This you cannot do now. I think this is a no go if we cannot find a
> > > > substitute for the lost functionality.
> > >
> > > We haven't lost much, since nearly everything that was in
> > > SpecialFunctions.h is now in UFL/FFC. What remains (e.g. FacetArea)
> > > could probably go in UFC eventually.
> >
> > FacetArea as in special function FacetArea?
> >
> > There are all kinds of functionalities in dolfin::Cell:
> >
> >    volume, diameter, normal, facet_area

diameter and normal are available through UFL (and so too could be 
volume and facet area, if not already).

> > which are neat functions to have within a more complex Expression.
> >
> > > What we can do is create a dolfin::Cell from a ufc::cell (since we can
> > > access the cell index from the ufc::cell object) if we know that the
> > > ufc::cell comes from the mesh at hand.
> >
> > How would a user access a dolfin::Cell from within eval?
>
> By storing a reference to the Mesh:
>
>    class MyExpression : public Expression
>    {
>    public:
>
>      MyExpression(const Mesh&  mesh) : mesh(mesh) {}
>
>      ...
>
>      void eval(...)
>      {
>        Cell cell(mesh, cell_index);
>        ...
>      }
>
>    private:
>
>      const Mesh&  mesh;
>
>    };

Exactly. We might also be able to provide a simple interface that 
supplies the cell (by doing the above in the background).

All we need is the cell index, and in some cases the local facet index 
too, to access everything that we could previously.

Garth

> --
> Anders
>
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