dolfin team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

On Monday May 30 2011 10:36:21 Anders Logg wrote:
> On Mon, May 30, 2011 at 10:24:48AM -0700, Johan Hake wrote:
> > On Monday May 30 2011 04:33:29 Martin Sandve Alnæs wrote:
> > > On 30 May 2011 12:51, Marie E. Rognes <meg@xxxxxxxxx> wrote:
> > > > On 05/30/2011 11:26 AM, Martin Sandve Alnæs wrote:
> > > >> Since this feature implementation relies on modifying immutable
> > > >> objects, I'm not the least surprised you're getting problems. The
> > > >> bug is not that dolfin subdomains are not passed with forms, but
> > > >> that they are allowed to be attached in the first place on an
> > > >> existing and assumed immutable form object.
> > > > 
> > > > Yes...
> > > > 
> > > >> The short term solution to this bug is to revert pydolfin back to
> > > >> providing subdomains as arguments to assemble and variationalproblem
> > > >> where they belong, instead of attaching them to forms. I think this
> > > >> should be done for fenics 1.0 if this bug is a problem.
> > > >> 
> > > >> Improvements to the language for expressing subdomains of various
> > > >> kinds is in the design stage, but that won't happen before the
> > > >> summer.
> > > > 
> > > > Specifications of subdomain does not belong as arguments to assemble
> > > > and variational problem. If you have a form
> > > > 
> > > >        L = g*v*dG
> > > > 
> > > > where G is a part of a boundary (In semi-math, semi-UFL notation), G
> > > > should be related to the form. Not to the matrix resulting from the
> > > > assembly of the form.
> > > > 
> > > > (cc to DOLFIN since the below involves DOLFIN mainly)
> > > > 
> > > > The interface to VariationalProblem
> > > > 
> > > >        VariationalProblem(., ., bcs, exterior_facet_domains,
> > > > 
> > > > interior_facet_domains, cell_facet_domains)
> > > > 
> > > > was rather suboptimal because it assumed implicitly that the bilinear
> > > > and the linear form were defined over the same subdomains. That in,
> > > > combination with dx = dx(0) etc, is highly bugprone.
> > > > 
> > > > I care of course because if you want to use the same patent for an
> > > > variational problem with automatic adaptivity, and take care of the
> > > > above, the required  input will look something like this
> > > > 
> > > >        VariationalProblem(., ., bcs,
> > > >        
> > > >                        primal_bilinear_exterior_facet_domains,
> > > >                        primal_bilinear_interior_facet_domains,
> > > >                        primal_bilinear_cell_domains,
> > > >                        primal_linear_exterior_facet_domains,
> > > >                        primal_linear_interior_facet_domains,
> > > >                        primal_linear_cell_domains,
> > > >                        goal_exterior_facet_domains,
> > > >                        goal_interior_facet_domains,
> > > >                        goal_cell_domains)
> > > > 
> > > > which I can't live with.
> > > > 
> > > > The Coefficient/Function magic must involve some of the same issues
> > > > as this. I imagine that a similar way of fixing it should be
> > > > possible.
> > > 
> > > I'm not saying it can't be implemented, only that it can't
> > > be implemented well within the FEniCS 1.0 timeframe, and
> > > that fixing the current solution will lead down a bad path.
> > > I'm hoping for a much better solution later this year, but
> > > that will require some design work first.
> > > 
> > > An alternative short term approach could be to attach the data to the
> > > measures.
> > > 
> > > dxp = dx(cell_domains=primal_cell_domains)
> > > dsp = ds(exterior_facet_domains=primal_exterior_facet_domains)
> > > L = g*dxp(1) + f*dsp(0)
> > > 
> > > and making sure that this data follows measure objects around.
> > > They can then be collected in ufl preprocess just like functions
> > > and function spaces. Then the connection between the
> > > meshfunction and the dx(i) index looks more explicit as well.
> > 
> > I like that syntax. I guess we only allow one type of cell integral
> > within one form?
> > 
> > My conserns regards changing the subdomains after creating the form, as
> > this can be a convinient way of reusing a compiled form. But I guess
> > letting domain arguments in assemble override domains in the form should
> > fix that.
> 
> I like the current syntax and would not like to change it again. An
> important point is that it allows the same syntax to be used in both
> Python and C++:

For the ufl/dolfin mixing we have quite a lot of syntax that already differ.

> a.exterior_facet_domains = exterior_facet_domains
> a.exterior_facet_domains = exterior_facet_domains;

We could still have the foo_domains argument to dolfin::Form. These gets 
populated the same way as previously in UFL/C++, but using the proposed syntax 
from Martin in the PyDOLFIN interface. Then in the dolfin.Form constructor, we 
extract the "attached" domains from the measures and reattach them to the 
generated cp.Form.

Johan

> This won't work with dx etc.
> 
> I suggest we keep the current syntax and find an improved
> implementation later.
> 
> --
> Anders
> 
> _______________________________________________
> Mailing list: https://launchpad.net/~dolfin
> Post to     : dolfin@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~dolfin
> More help   : https://help.launchpad.net/ListHelp