“…For time-varying systems, expect for some special cases, the Lasalle invariant principle is either not valid or difficult to use [49]. Hence, some researchers attempt to use the available Lyapunov function, whose time-derivative is not strictly negative definite, to construct a new Lyapunov function whose time-derivative is negative definite ( [1,3,4,34,39]). One could hope that a method for proving the existence of a Lyapunov function might carry with it a constructive method for obtaining this function.…”