dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Mon, Apr 12, 2010 at 08:32:41AM -0700, Johan Hake wrote:
> On Monday April 12 2010 08:14:09 Kristian Oelgaard wrote:
> > 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.
>
> What would the default subdomain then be which we integrate over when a
> SubDomain is passed?
>
> I don't know if I really get what you are trying to accomplish.
>
> Whould:
>
>   f*ds + g*ds(0) + h*ds(1)
>
> create three integrals one for "subdomain" -1 which returns the integral over
> all subdomains, and one for each of 0 and 1.

Yes.

> Sounds like this is best managed above the UFC/UFL layer.

Yes, but I don't see how that should be done. Somehow we need to pass
the information from

  f*ds + g*ds(0) + h*ds(1)

to the assembler.

One option would be to add f*ds to all the sub integrals. So we don't
change the UFC interface (or DOLFIN) but do the following:

1. ds = ds(-1)

2. FFC adds ds(-1) to all its sub domain integrals.

> > > 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.
>
> No, this is correct. But I think it is suboptimal. When create_cell_integral
> is called using 1 as argument the zero pointer is returned. Dolfin then needs
> to check this. It would be more intuitive to let ufc check it, and to expand
> ufc with foo_integral_markers(uint * markers) or something. But it might as
> well not be worth the ufc update.

It's a very easy check for DOLFIN and it avoids adding an extra
function to UFC

--
Anders


> Johan
>
>
> > > 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
> >

Attachment: signature.asc
Description: Digital signature