dolfin team mailing list archive

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

2008/9/6 Garth N. Wells <gnw20@xxxxxxxxx>:
>
>
> Dag Lindbo wrote:
>> Anders Logg wrote:
>>> There seems to be a problem (among many) with the current design of
>>> the Function classes (see thread "evaluating higher order mesh function").
>>>
>>> In particular, the finite element is missing in DiscreteFunction. My
>>> suggestion would be to just add it and let a DiscreteFunction consist
>>> of the following four items which are always available:
>>>
>>>   mesh, x, dof_map, finite_element
>>>
>>> Is this enough, and what other issues to we need to fix?
>>>
>>
>> One major issue which I just want to reiterate is ownership of data. As
>> it stands, the DiscreteFunction may or may not be responsible for e.g.
>> the dof vector x, depending on whether local_vector is a NULL pointer or
>> not. Take a look at the thread "Ownership" from Garth on 06/26/2008.
>>
>
> Yes, this is a big problem and has caused me a few headaches with bugs.
> For example, passing a user-defined Function to a function to convert it
> to a DiscreteFunction via a projection onto a finite element basis
> causes a problem because the FiniteElement which the projected Function
> points to goes out of scope once the function is exited.
>
>> A problem related to this is initialization of the DiscreteFunction. We
>> had a bug previously where the LinearPDE class maintained ownership of
>> the solution vector. The only way to prevent this was to break the
>> encapsulation of DiscreteFunction by making it a friend of LinearPDE (as
>> with XMLFile for the same reasons). Here is some of the code that
>> handles this initializaton today (L101 in LinearPDE.cpp):
>>
>>   u.init(mesh, *x, a, 1);
>>   DiscreteFunction& uu = dynamic_cast<DiscreteFunction&>(*u.f);
>>   uu.local_vector = x;
>>
>> This ain't poetry in my opinion :)
>>
>
> Indeed, this isn't nice, and there is something similar in XMLFile.cpp.
>
> Garth

We should start to use std::tr1::shared_ptr. There is some support for it
with python in swig 1.3.35, which is part of the upcoming Ubuntu Intrepid

--
Martin