Dear Firedrake(rs),

I am considering a "standard" FEM problem with the following variables h(chi,tau) and phi(chi,tau) as function of transformed coordinate chi and time tau in chi=[0,L].

In the weak formulation, the point value h(Lp,tau), so the function value at 0<chi=Lp<L

as well as, of course, the function h(chi,tau) appear in the space integral of the weak form.

In essence, due to a transformed moving boundary this point evaluation arises.

I can formulate the detailed (nonlinear) matrix-vector FEM and its time discretisation

because after the expansion of h(chi,tau) the coefficients h_j(tau) appear

and h(Lp,tau) = h_Np(tau) for j =Np, say, such that the distinction between function

and point values disappears.

I am struggling to see how I can do this on the weak form level in firedrake.

It would work in integral form by using a delta function after introducing h(Lp,tau)

as an auxiliary scalar variable but I assume that is not available?

What is the FD-tactic here which one can employ?

Thank you and best wishes,

Onno