Assembling forms defined at the boundary

Question

I want to explicitly assemble forms of the type
$$
v\mapsto \int_\Gamma (\partial_n v) \phi d\gamma
$$
where $\Gamma$ is the boundary of the domain $\Omega \in \mathbb R^2$, where the scalar trial function $v$ and the testfunction $\phi$ is defined on. By $\partial_n v$, I denote the normal derivative of $v$.

How can I do this?

Answer 1

Hi Jan,
Are you trying to implement a Neumann boundary condition? In that case the
Neumann boundary demo can help you

Otherwise if you want to get an integrated Neumann value after you have solved a PDE
you can do

assemble(g*v*ds)

where g is the solution of your PDE and v a test function object.

Comments

Thank you for the hint. My problem goes beyond applying Neumann BCs, but with some manual work this should be doable using the ds measure.

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The link is fixed now.