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[Anders Logg <logg@xxxxxxxxx>]

On Tue, Jun 03, 2008 at 11:24:54PM +0200, Evan Lezar wrote:
> The problem is that I am not quite sure how to use it ...
> 
> The code I have at the moment is as follows:
> 
>     mesh = UnitSquare(1,1)
> 
>     mesh.refine()
>     mesh.refine()
> 
>     element = FiniteElement("Nedelec", "triangle", order);
> 
>     v = TestFunction(element)
>     u = TrialFunction(element)
> 
>     # assemble the mass and stiffness matrices
>     # the bilinear form is defined as the transverse curl since it is
> a two dimensional problem
>     # a = dot(curl(v), curl(u))
>     a = (vec(v.dx(0))[1] - vec(v.dx(1))[0])*(vec(u.dx(0))[1] - vec(u.dx(1))[0])
> 
>     (S) = assemble(a*dx, mesh)
>     (T) = assemble(dot(v, u)*dx, mesh)
> 
> I then use S and T to solve the eigenvalue system S x = lambda T x
> 
> The reason I am having trouble is that this does not use the pde class
> and I have not found an example that uses the DirichletBC class to
> specify the boundary conditions for matrix assembly.
> 
> Thanks for the quick reply
> Evan

Hmm... I realize now I don't know how to set boundary conditions for
an eigenvalue problem (other than by eliminating unknowns). For
homogeneous boundary conditions, I guess one could zero out a row in
S, insert a 1 on the diagonal and zero out the corresponding row in T.

There is an example of applying boundary conditions in

 demo/pde/convection-diffusion/python/demo.py

but it is for a linear system Ax = b. There is also a function zero()
in DirichletBC which can be used to zero out a row in a matrix.

-- 
Anders