ufl team mailing list archive

[Kent-Andre Mardal <kent-and@xxxxxxxxx>]

tor, 19.06.2008 kl. 11.38 +0200, skrev Martin Sandve Alnæs:
> 2008/6/19 Kent-Andre Mardal <kent-and@xxxxxxxxx>:
> >
> > Should we include Dirichlet conditions in UFL ?
> >
> > It could be done with the notion of traces:
> >
> > g = Function(...)
> > u = TrialFunction(...)
> > T = FacetTrace(...)
> 
> From a programming point of view, this line makes no sense to me:
> 
> > T*u = g
> 
> What it means mathematically is clear, but this can never be valid Python.

You're right. Maybe 
T*u == g. 
Is this possible in Python ? It is in C++... 


> 
> Do you mean something like:
> 
> a = u*v*dx + dot(u,n)*v*ds(0) + g*T(1)
> 
> where T(i) and ds(i) would refer to the same boundary?
> 

Could be but I think this is less mathematically clear 
(for one thing a would not be bilinear)

c = T*u == g. 
a = u*v*dx + dot(u,n)*v*ds(0)


> 
> > meaning that u = g on the boundary.
> > One could also have T(i) for the trace
> > on subdomain i.
> >
> > I think it also could be put into the UFC assembly loop in a nice way,
> >
> > assembly(...){
> >
> >  ...
> >
> >  assembleCells(...);
> >
> >  assembleExteriorFacets(...);
> >
> >  assembleInteriorFacets(...);
> >
> >  enforceTraces(...);
> >
> > }
> >
> >
> > The bad thing is that it affects both the right and left hand side so
> > that the matrix and the right hand side need to be assembled at the same
> > time (or one could make a very sparse matrix that resemble applying the
> > constraints).
> >
> > Kent
> 
> I don't think they'll _need to_ be assembled at the same time, this could
> also be ignored during initial assembly and then done as a separate step.
> In particular if it's only part of UFL and not UFC: the Assembler shouldn't
> know about UFL at all, only UFC (which we may of course extend as well!).
> 
> --
> Martin