dolfin team mailing list archive

[Martin Sandve Alnæs <martinal@xxxxxxxxx>]

On Thu, May 7, 2009 at 10:34 PM, Garth N. Wells <gnw20@xxxxxxxxx> wrote:
>
>
> Martin Sandve Alnæs wrote:
>>
>> On Thu, May 7, 2009 at 9:43 PM, Garth N. Wells <gnw20@xxxxxxxxx> wrote:
>>>
>>> Anders Logg wrote:
>>>>
>>>> I've added some of the requested features to the parameter system,
>>>> some pushed and some sitting here in a local repository. But the
>>>> current design makes it a pain to add new features. A single change
>>>> will make it necessary to add a function in at least 5 different
>>>> classes.
>>>>
>>>> So I'm thinking of reimplementing and simplifying the parameter
>>>> system. I think I know how to make it simpler.
>>>>
>>>> But before I do that, does anyone have opinions on the
>>>> design/implementation? Is there any third-party library that we
>>>> could/should use (maybe something in boost)?
>>>>
>>> This could be interesting:
>>>
>>>  http://www.boost.org/doc/libs/1_39_0/doc/html/program_options.html
>>>
>>>
>>> While we're on the topic of boost, this is neat
>>>
>>>  http://www.boost.org/doc/libs/1_39_0/libs/parameter/doc/html/index.html
>>>
>>> It addresses the problem we had with attaching functions to forms -
>>> arguments can associated with a name. At first glance it allows
>>>
>>>  BilinearForm a(V, V, "f", f, "h", h);
>>>
>>> or
>>>
>>>   BilinearForm a(V, V, "h", h, "f", f);
>>>
>>> so the user doesn't need to worry about the order of the arguments.
>>
>> We don't have that problem with code generated by dolfin_utils.wrappers:
>>
>>    BilinearForm a(V, V):
>>    a.f = f;
>>    a.h = h;
>>
>
> It was a problem and the above approach is how we resolved it. It doesn't
> however work well for mixed elements. This still needs to be resolved. Are

I see, for example:
  u, p = Functions(TH)
would make both u and p Indexed instances so their names won't be found.

The workaround for now is to use

  up = Function(TH)
  u, p = split(up)

which will properly name the mixed function "up" (not u and p).

I suspect better subfunction support in both DOLFIN and UFL is
needed for this and other important mixed element features.


> there names which could be used for a Function in Python (like 'default')
> which are not legal in C++?

Good point. But probably not a big problem. We could add checks
for C++ language keywords in dolfin_utils to give proper error messages.


>> or:
>>
>>    CoefficientSet coeffs;
>>    coeffs.u       = u;
>>    coeffs.dt      = dt;
>>    coeffs.beta    = beta;
>>    BilinearForm a(V, V, coeffs);
>>    LinearForm L(V, coeffs);
>>
>
> . . . which looks like it hasn't been fully implemented. It would fix the
> problem that in order to do
>
>  Form* my_form = new MyForm(V, V);
>  my_form.a = a;
>
> we had to keep the old-style constructor in the generated code.

CoefficientSet works fine for me, but I don't think FFC uses dolfin_utils yet?

Martin