dolfin team mailing list archive

[Kristian Oelgaard <k.b.oelgaard@xxxxxxxxx>]

On 12 April 2010 15:56, Anders Logg <logg@xxxxxxxxx> wrote:
> On Thu, Apr 08, 2010 at 08:44:21AM -0700, Johan Hake wrote:
> > On Thursday April 8 2010 08:36:24 Marie Rognes wrote:
> > > Johan Hake wrote:
> > > > On Thursday April 8 2010 04:51:24 Marie Rognes wrote:
> > > >> There is something suboptimal with regard to assembly over sub_domains
> > > >> specified
> > > >> by domains (in contrast to markers)
> > > >>
> > > >> Say I have some functional
> > > >>
> > > >> (*)    M = f*ds
> > > >>
> > > >> where f is some function. Let 'domain' be some sub-domain.
> > > >>
> > > >> Now, it is not clear to me what
> > > >>
> > > >>     v = assemble(M, mesh=mesh, exterior_facet_domains=domain)
> > > >>
> > > >> gives. It would be really convenient (for my purposes) if it gave
> > > >> the same as
> > > >>
> > > >>     v = assemble(M, mesh=mesh)
> > > >
> > > > Considering that ds defaults to ds(0) I think it is a logical behaviour.
> > >
> > > So
> > >
> > >     ds == ds(0)
> > >
> > > ?
> >
> > In ufl/objects.py
> >
> >   ds = Measure(Measure.EXTERIOR_FACET, 0)
> >
> > So I guess yes.
>
> Yes, this is the case.
>
> I think the current behavior is correct, if one knows that ds = ds(0).
>
> But I understand it can be confusing. Marie and I discussed this last
> week and I suggested that we let
>
>  ds = ds(-1)
>
> and that should denote integration over all sub domains, and ds(0)
> would mean integration specifically over sub domain 0.
>
> I was going to suggest this but I realize now we would need to change
> the UFC interface (and FFC). It is currently based on the function
>
>  num_foo_integrals

BTW, is there a bug in the code generation for this function? If I do:
element = FiniteElement("Lagrange", triangle, 1)
f = Coefficient(element)
M = inner(f, f)*dx + inner(f, f)*dx(2)

the return value of num_cell_integrals is 3, but create_cell_integral(), only return an integral in case 0 and 2.

> returning the number of integrals and
>
>  create_foo_integral(i)
>
> returning the integral for the terms on sub domain i.
>
> This would need to be extended, possibly by overloading with
>
>  create_foo_integral()
>
> which would return the terms that are present on all sub domains.

Should it return an array of integrals over sub domains, or one integral like:
Integrand_0*dx(0) + Integrand_1*dx(1) --> (Integrand_0 + Integrand_1)*dx(-1) ?
The second option will result in a lot of redundant code being generated.

> Is it worth the effort of updating ufc.h, the UFC manual, the
> assembler and FFC?

No.

Kristian

> --
> Anders
>
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