Mathematical Problems in Engineering
By unifying the method of variation of parameters and Lyapunov's second method, we develop a fruitful technique which we call variational Lyapunov method. We then consider the stability theory in this new framework showing the advantage of this unification.
Lakshmikantham, V., Liu, X., & Leela, S. (1998). Variational lyapunov method and stability theory. Mathematical Problems in Engineering, 3(6), 555-571. doi:10.1155/S1024123X97000689