dolfin team mailing list archive

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

2008/9/8 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?
>>
>
> I'm not sure I agree that the dof map and finite element should be owned
> by the discrete function. There was a great suggestion from Martin, in a
> thread "Abstraction idea" from 06/05/2008, to create a class
> FunctionSpace where the mesh, element and dof_map(s) are aggregated.
> Citing Martin:
> U = FunctionSpace(mesh, dofmapset, form, 0) # or something similar
> u = Function(U)
> v = Function(U)
>
> This seems a solid approach to me since it would provide a way of
> encapsulating the mathematical formulation of the problem, which is more
> or less const and likely to be reused by many discrete functions in a
> solver.
>
> It seems to me that there is an obvious risk that a lot of redundant
> initialization would occur if all discrete functions should own their
> own elements and dof maps. There seems to be consensus that the mesh
> should be "global" for efficiency reasons, so why not treat the function
> space the same way?
>
> Is there a problem with an approach where the funciton _always_ owns the
> vector and _never_ owns the function space (and mesh)? A very strict
> design would avoid shared/smart pointers, provide a comprehensible user
> interface and probably help the parallellization effort.
>
> /Dag

If the Function always owns the vector, there are cases you'll have to
make unneccessary copies of a vector, in particular such scenarios
may occur when trying to combine dolfin with something else.

If the Function never owns the function space, it must always be
constructed explicitly by the user. This may not be a bad thing.
However, if the Function is loaded from a file, nobody owns the
FunctionSpace.

--
Martin