dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

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
>
> 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;

  };

--
Anders