dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Mon, Jan 26, 2009 at 11:30:25AM -0500, Shawn Walker wrote:
> Hello, I have a question on implementing the Laplace-Beltrami operator in 
> FFC/DOLFIN.  Can you do it?  If the domain is just a 2-D surface, then 
> maybe not; 2-D topological meshes in 3-D geometric space still needs to be 
> implemented right?

The mesh class supports it (that's why you can extract the boundary
mesh from a 3D mesh) but other pieces are missing.

I suggest you try a very simple problem and try to track where things
go wrong (I assume they will). It might be that major work will be
needed to get it to work, but it might also be fixable.

> What about if I just have a 2-D (flat) domain with a 1-D boundary.  Is 
> there a convenient way to define the surface (tangential) gradient in FFC? 
> It is just the derivative with respect to arc-length multiplied by the 
> tangent vector.  Can you define forms on the boundary like that?

Do you want to have the tangent on the boundary? That's fairly easy,
just do

 n = FacetNormal(mesh)
 t = [-n[0], n[1]]

-- 
Anders

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