Stella uses a digital computer to simulate an analog process. I have
also used analog computers (inductors, capacitors, resistors...but NO
transistors) to simulate car suspensions and nuclear reactors.
If the differential equations of two systems are the same, it doesn't
matter whether you're talking about electrical currents or the money
supply -- the behavior of the model will predict that of the actual
system. Remind me to show you my isomorphism party trick (it's
interactive, can't do it by email).
Sean Morgan