On the Method of Vector Lyapunov Functions
The method of vector Lyapunov functions consists of employing several Lyapunov-like functions and the theory of vectorial differential inequalities. This general comparison technic leads to a more flexible mechanism to study the qualitative properties of nonlinear differential systems. This method is also effective in discussing interconnected dynamical systems where a construction of a single Lyapunov function is difficult. However, an unpleasant fact in this approach is the requirement of quasimonotone property of the comparison system. An idea to get around this will be indicated which might be useful in applications. Also, an extension of this technic to abstract cones will be discussed.