ufl team mailing list archive

[Martin Sandve Alnæs <martinal@xxxxxxxxx>]

On Tue, Jul 7, 2009 at 9:47 PM, Anders Logg<logg@xxxxxxxxx> wrote:
> On Tue, Jul 07, 2009 at 08:48:17PM +0200, Martin Sandve Alnæs wrote:
>> On Tue, Jul 7, 2009 at 5:52 PM, Kristian
>> Oelgaard<k.b.oelgaard@xxxxxxxxxx> wrote:
>> > Quoting Martin Sandve Alnæs <martinal@xxxxxxxxx>:
>> >
>> >> On Wed, Jun 17, 2009 at 5:15 PM, Anders Logg<logg@xxxxxxxxx> wrote:
>> >> > On Wed, Jun 17, 2009 at 03:32:03PM +0200, UFL wrote:
>> >> >> One or more new changesets pushed to the primary ufl repository.
>> >> >> A short summary of the last three changesets is included below.
>> >> >>
>> >> >> changeset:   908:ef256e35e417096ae9b9d3a7e915e27e6971ae3f
>> >> >> tag:         tip
>> >> >> user:        "Martin Sandve Alnæs <martinal@xxxxxxxxx>"
>> >> >> date:        Wed Jun 17 15:32:01 2009 +0200
>> >> >> files:       test/newtests/test_demos/test_demos.py
>> >> test/newtests/test_elements/test_elements.py
>> >> test/newtests/test_exprbasics/test_construction.py ufl/__init__.py
>> >> ufl/exproperators.py ufl/finiteelement.py ufl/function.py
>> >> >> description:
>> >> >> Added ElementRestriction class with notation "Vr = V[dx(k)]".
>> >> >
>> >> > What does this mean? What is V?
>> >> >
>> >>
>> >> The restriction of a function space to a domain.
>> >> Obviously the use of the measure "dx" is an
>> >> abuse of concepts, but it's convenient to reuse it.
>> >>
>> >> Consider:
>> >>
>> >> V1 = FiniteElement("CG", cell, 1)
>> >> V0 = FiniteElement("DG", cell, 0)
>> >> V = V1 + V0[ds(2)]
>> >> u, lamda = TrialFunctions(V)
>> >>
>> >> Here lamda lives only on boundary 2.
>> >>
>> >> Of course, this is useless without support in the rest of
>> >> FEniCS, so it's only a proof of concept for input syntax.
>> >>
>> >> Feel free to suggest alternative syntax and naming.
>> >
>> > First of all, any ideas on how to implement support for this in say FFC?
>>
>> No. It will probably require non-trivial extensions to
>> UFC and DOLFIN as well, and seems like a fairly
>> complicated design task to get it general enough.
>>
>> > In relation to this new functionality.
>> > If we want to restrict an element, not to a particular subdomain, but to the
>> > exterior of each element, i.e., only consider the dofs that live on facets,
>> > would that also fit in this framework?
>> > Should the syntax for this be V[ds + dS]?
>> > But then what should the syntax be for only considering dofs that live
>> > internally on the cell?
>> >
>> > Or, if V is defined on 'triangle', then one could do
>> > V['interval'] to get the facet dofs, and V['triangle'] to get the interior dofs.
>> > It would even be possible to do V['vertex']. If we also allow this syntax we can
>> > restrict elements with respect to either Cells or Measure.
>> > Could this work?
>> >
>> > How can this be implemented in FFC? In the case of V['interval'], we could get
>> > the finite element from FIAT as usual, and then find all dofs NOT on the facet
>> > and dump them in a list of dofs that should be ignored when generating all the
>> > code.
>> >
>> > Kristian
>>
>> The use of Measure to represent a domain didn't feel
>> right to begin with. Seems like it's not general enough
>> anyway, so I suggest designing a separate abstraction
>> for description of subdomains or subsets of dofs.
>>
>> My guess is that this task will require some
>> design iterations to make it good.
>>
>> I won't be around to see this through though,
>> since I'm beginning in another job in august.
>
> Where?
>
> --
> Anders

At TANDBERG, as audio programmer for video conferencing systems.

Martin