dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Sun, Sep 02, 2012 at 11:23:11AM +0100, Garth N. Wells wrote:
> On 2 September 2012 11:10, Anders Logg <logg@xxxxxxxxx> wrote:
> > On Sat, Sep 01, 2012 at 03:09:42PM +0100, Garth N. Wells wrote:
> >> The logic around how we handle integration over domains is confusing.
> >> I'm trying to fix a small problem which is opening a can of worms.
> >> Subdomain data can be optionally passed to the assembler, attached to
> >> a Form or attached to a Mesh (the latter being particularly confusing
> >> because it's mixing concepts). I suggest that we have just one to do
> >> things, and I think the most logical and user friendly is to attach
> >> subdomain data to Forms. Opinions?
> >
> > I agree that the logic is complex, but it is there for a reason.
> >
> > There are three ways to specify subdomains, by order of increasing
> > priority.
> >
> > First, it can be specified as part of the mesh. This is a good thing
> > since it allows markers to be stored as part of Mesh XML files. Very
> > useful for Mesh generators and tools like VMTK.
> >
>
> I think that this is very clumsy and mixes concepts. Say I have one
> mesh but want to perform two different simulations with different bcs.
> It's opaque. What happens if I have markers in a Mesh and markers
> attached to a Form -> ambiguous.
>
> Better would be to store the markers as part of the mesh, but pull
> them out and attach them to a form. I was already planning to have
> mesh markers in a mesh file that are identified by strings (e.g.
> "top", "inner sphere", etc) rather than  integers (which are error
> prone because they convey no meaning). A user could query which
> markers a mesh has (via a set of identifier strings), and attach the
> right ones.

Sounds like a good solution. We could add a simple function call for
transferring the markers "as is" to the Form, if the mesh is already
marked with the correct integers to be used in the Form. A potential
problem with this approach is the duplication of data (markers in both
Mesh and Form). Possibly, this could be handled with shared pointers.

> > Second, it can be specified as part of a Form. This is useful for
> > assembling several forms on the same mesh but with different domains.
> >
>
> This is nice.
>
> > Third, it can be specified explicitly as an argument to the assembler.
> >
> > If we should cut any of these, I would suggest cutting the third one,
> > but I think it is widely used as part of both user code and examples
> > so I'm not sure we should cut it.
> >
>
> We have a bug that I'm more interested in fixing simply and robustly
> than in preserving a clumsy interface, so I'd cut it. Users can update
> their code.

We should wait for comments on this one. I can manage without those
extra arguments, but I believe others use it.

--
Anders