time dependent gain

I am working on a RLC circuit (three RLC circuits to be exact, linked together). They are series - basically the same as the matlab/simulink RLC example. I would like to make R=f(k,t) where k is the results of the circuit "upstream" and of the prior time step of R (so that R is incrementally changing). The same goes with L and C. Is there an example m code that shows how that can be implemented? It doesn't have to be my example - specifically, I think I can make it work if I know how to control the time step in the m file....