ffc team mailing list archive

[Jed Brown <jed@xxxxxxxx>]

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.

Jed

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