dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Fri, Jun 06, 2008 at 02:30:12PM +0200, Martin Sandve Alnæs wrote:
> 2008/6/6 Anders Logg <logg@xxxxxxxxx>:
> > On Fri, Jun 06, 2008 at 01:40:15PM +0200, Martin Sandve Alnæs wrote:
> >> 2008/6/6 Johan Hake <hake@xxxxxxxxx>:
> >> > On Friday 06 June 2008 13:19:54 Martin Sandve Alnæs wrote:
> >> >> Say I have a form
> >> >>
> >> >> a = u*v*dx + f*v*ds
> >> >
> >> > Isn't it possible to do
> >> >
> >> > a = u*v*dx + f0*v*ds0 + f1*v*ds1
> >> >
> >> > Johan
> >>
> >> Sure, but my forms are more complicated than that,
> >> and it would add to the compilation time for the forms.
> >
> > Well, there are two options:
> >
> > 1. Use two subdomains and two Functions, one on each domain.
> >
> > 2. Use one subdomain and one Function for the whole domain.
> >
> > If you think (1) costs too much, then you need to define your Function
> > in such a way that it is takes care of the different domains. I guess
> > it should be possible to create one Function f which owns two
> > Functions f0 and f1, overload interpolate() for f and there send the
> > data on to either f0 or f1.
> >
> > We could add an interface for this, something like
> >
> >  f = Function([f0, f1, f2, ...], sub_domains)
> >
> > but it seems overly complicated and specific.
> 
> Yes, it quickly becomes very complicated.
> 
> Another solution could be to add an argument
> "bool zero_tensor=true" next to reset_tensor in
> assemble functions, define a separate form
> with just the boundary integral, and call assemble
> repeatedly for each coefficient set with zero_tensor=false.
> This would be much efficient if iteration directly
> over a subdomain was possible, which will require
> the "inverse" of a MeshFunction.

I don't understand why this would be faster than just defining the form

  a = f0*v*ds0 + f1*v*ds1

(if we assume that we also here have access to the inverse of the
MeshFunction).

-- 
Anders

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