where u (t) is an input signal, y (t) is an output signal, the vector x represents a set of n state variables describing the device, and g and f are continuous functions. For a current-controlled memristive system the signal u (t) represents the current signal i (t) and the signal y (t) represents the voltage signal v (t). For a voltage-controlled memristive system the signal u (t) represents the voltage signal v (t) and the signal y (t) represents the current signal i (t).