dolfin team mailing list archive

["Martin Sandve Alnæs" <martinal@xxxxxxxxx>]

2008/10/30 Johan Hake <hake@xxxxxxxxx>:
> On Thursday 30 October 2008 19:20:06 Anders Logg wrote:
>> Most things are now in place, finally. At least we can run the Poisson
>> demo again... :-)
>>
>> Anyway, take a look at demo/pde/poisson/main.cpp and see what you
>> think. I think it looks pretty good, but please report if you have any
>> ideas for further improvements of the interface while we're at it.
>
> It looks nice, but I see some magic which I wish you can shed some light on.
>
> The introduction of PoissionFunctionSpace is not clear for me. Why do we have
> to instantiate the forms with it?

Such that the Forms can use the same FunctionSpaces as are used in the
rest of the code, while the user stays in control of their allocation.
In particular, DofMaps needs to be shared between different parts of the code.

> In the form file the two forms L and a are defined. These are then reflected
> in the main.cpp file as before. This is intuitive. But where does the
> PoissonFunctionSpace come from? I as a user has not defined it in the form
> file.
>
> It might help if we introduce the notion of FunctionSpace in FFC/UFL. Then
> some of the magic would disapear I think.

This could reinforce the problem with circular dependencies I mentioned
earlier. I don't see that anyone has adressed that issue.

> The talk about a Function always knowing its Space was clear, you can always
> plot it, and so on. But then the introduction of the "magic" dedication of
> FunctionSpace broke that, and also made the actuall function of FunctionSpace
> more blurry.
>
> Intuitively I would prefer:
>
>  ...
>  PoissonFunctionSpace V(mesh);
>
>  Source f(V);
>  Flux g(V);
>
>  PoissonBilinearForm a();
>  PoissonLinearForm L();
>
>  L.set_f(f); L.set_g(g);
>  ...
>
> If this is not possible or if it is but we do not want it, please inform me.

We would still need

  PoissonBilinearForm a(V,V);
  PoissonLinearForm L(V);

Which looks, I agree, a bit misleading since you cannot
pass any other function spaces to these forms.

>> Any help with getting the remaining demos and the Python interface
>> working again appreciated.
>
> I could probably help with getting the python interface up and going, at least
> with the metaclass stuff discussed earlier.
>
>
> Johan


--
Martin