A nonlinear second-order system in the form of an electrical circuit. i is electrical current, and v
is voltage difference between each end of C. The value of the resistor (R) in this figure is dependant on i as well as v
whereas the capacitor (C) and the inductor (L) are dependent only on v
. Vin(t) is a voltage source for this simple circuit system. Nonlinear circuit elements in this circuit imply the nonlinearity of fig. 1 (c).