Comment 10 for bug 1077912

Probably not, so thanks for the bug report. :-)

--
Anders

On Tue, Nov 13, 2012 at 07:29:13PM -0000, Martin Sandve Alnæs wrote:
> Ok, great :) Is there a better place to report documentation errors than
> as bugs?
>
> Martin
>
> Den 13. nov. 2012 kl. 19:22 skrev Anders Logg <email address hidden>:
>
> > I agree it may be confusing and I can clarify this in the
> > documentation. But I would not call this a bug. It is a well-known
> > feature that DirichletBC can be used to set "boundary conditions"
> > anywhere. It's been like that for ca 10 years. That's also why we have
> > the on_boundary parameter to allow setting conditions on the actual
> > boundary.
> >
> >> Boundary (topology), the closure minus the interior of a subset of a
> >> topological space; an edge in the topology of manifolds, as in the case
> >> of a 'manifold with boundary'
> >>
> >> As I said above, this is at the very least a documentation bug. The
> >> sentence I quote makes no sense when all facets may be considered on the
> >> boundary. I.e. "a facet that is entirely on the boundary". An
> >> alternative interpretation of what "boundary" means also does not match
> >> the on_boundary argument to subdomain.inside. And BoundaryMesh takes the
> >> exterior boundary. Right? So some clarification of terms is in order, at
> >> least in the DirichletBC documentation.
> >>
> >> Martin
> >>
> >> Den 13. nov. 2012 kl. 10:12 skrev Anders Logg <email address hidden>:
> >>
> >>> This is not a bug. The problem is the interpretation of what boundary
> >>> means. The boundary is whatever the user specifies and it can lie in
> >>> the interior.
> >>>
> >>>> Public bug reported:
> >>>>
> >>>> According to
> >>>>
> >>>> http://fenicsproject.org/documentation/dolfin/1.0.0/python/programmers-
> >>>> reference/fem/bcs/DirichletBC.html#dolfin.fem.bcs.DirichletBC
> >>>>
> >>>> "The topological approach is faster, but will only identify degrees of
> >>>> freedom that are located on a facet that is entirely on the boundary."
> >>>>
> >>>> However, this does not seem to be the case. I will attach here a code
> >>>> which changes behaviour when switching between marking all facets or all
> >>>> facets on the boundary, look for the lines:
> >>>>
> >>>> if enable_bug:
> >>>> boundaries.set_all(walldomain)
> >>>> else:
> >>>> Wall().mark(boundaries, walldomain)
> >>>>
> >>>> ** Affects: dolfin
> >>>> Importance: Undecided
> >>>> Status: New
> >>>>
> >>>
> >>
> >
>