ffc team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Thu, Apr 16, 2009 at 07:56:32PM +0200, Jed Brown wrote:
> On Thu 2009-04-16 19:45, Anders Logg wrote:
> > On Thu, Apr 16, 2009 at 10:42:08AM -0400, Shawn Walker wrote:
> > > Hello.
> > > 
> > > I was wondering how do you have finite element spaces that only live on 
> > > the boundary?  Say I want to solve a mixed form for Laplace's equation. 
> > > And, I would like to set the normal flux on the boundary by using a 
> > > Lagrange multiplier that is only defined on the boundary.  Is there an 
> > > example on this already?
> > 
> > Is it not enough to add a boundary integral? Something like
> > 
> >   lmbda*(dot(sigma, n) - g)*ds
> 
> You seem to be describing a penalty method which doesn't add any dofs
> and can be enforced this way (just choose 'lmbda' to be a big number).
> The issue is that lmbda needs to have a suitable number of degrees of
> freedom in the global system and these need to correspond to basis
> functions on the boundary.

ok, now I see what you mean.

No, that's not possible to do (mixing function spaces on different
meshes in the same formulation).

-- 
Anders

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