dolfin team mailing list archive

[Dag Lindbo <dag@xxxxxxxxxx>]

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.

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 :)

/Dag

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