I had to look into companion (discrete-time) models for simulating saturable inductors in real-time on FPGA at work. The same week, a friend asked out of curio

I had to look into companion (discrete-time) models for simulating saturable inductors in real-time on FPGA at work. The same week, a friend asked out of curiosity where the inductor equation came from. It had been quite a while for me, so I found interesting to sit down and derive it from first principles (Maxwell's equations). I needed to create a simple continuous nonlinear model anyway for validating the discrete models.