Coupled ODE to PDE with Method of lines

Dear all,

i do have a PDE which describes sedimentation. I do discretize it in space and end up with a system of ode´s. Fairly simple.

Now i use the same PDE (settling of particles) inside a syringe (no particles leave the syringe) and move the piston (pressure filtration). Therfore i do have a moving boundary at the piston. So i have to solve for the piston height too.

The system looks like

dh/dt=(height(n+1)-height(n))/dt

dy/dt= dh/dt*(something discretized) + h(n)/h(n+1)*(something discretized)

My question is if i can put dh/dt and dy/dt in a vector and treat it as a coupled system of ode´s ? Could someone give me a hint how to code that ?

E.g

i=1:N
dydt=dydt(N+1)*(something discretized) + ???*(something discretized)
i=N+1
dydt=myOdePistonheight

So if the height variable is part of my input array y0 how do i get h(n+1)/h(n)

Sincerly

Moritz

[Moritz]

and i should add that one boundary in fact is an algebraic equation.

[Moritz]

so dde23 could be an option ?

[Moritz]

No one ?