dolfin team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

On Saturday March 27 2010 05:54:46 Jack wrote:
> New question #105698 on DOLFIN:
> https://answers.launchpad.net/dolfin/+question/105698
> 
> Dear all
> 
> I'm trying to solve the following problem:
> 
> -d/dx(du/dx) - (du/dx)^3 = 0   on 0 < x < 1
> 
> subject to the following bcs:
> 
> @ x= 0:    du/dx + u = 3/sqrt(2)
> @ x = 1:   du/dx = 0.5
> 
> I have in my ufl file:
> L  = inner(grad(v), grad(u))*dx - v*( (u.dx(0))**3 )*dx -
> v*((1.5*sqrt(2)-u))*ds(0) - v*(0.5)*ds(1)
> 
> I assume that ufl doesn't know about the boundaries, so in main.cpp, I have
> marked them like so: MeshFunction<dolfin::uint> boundaries(mesh,
> mesh.topology().dim()-1);
> 
> 	LeftNeumannBoundary boundaryL;
> 	boundaryL.mark(boundaries, 0);
> 
> 	RightNeumannBoundary boundaryR;
> 	boundaryR.mark(boundaries, 1);
> 
> The problem is how to use the VariationalProblem class. It requires the
> dirichlet bc, the cell_domains, the interior and exterior_facet_domains.

Just pass boundaries as exterior_facet_domains and DOLFIN will assemble the 
correct forms at the marked boundaries.

Johan

> How can I use VariationalProblem without specifying the dirichlet bc?
> 
> Thanks
> 
> Jack