dolfin team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

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.

Johan

> Martin
> 
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