1. R. Courant and D. Hilbert, Methods of Mathematical Physics (Gostekhizdat, Moscow, 1951), Vol. 1 [in Russian].
2. L. D. Akulenko and G. V. Kostin, “The Perturbation Method in the Problem of Dynamics of Nonuniform Elastic Rods,” Prikl. Mat. Mekh. 56(3), 452–464 (1992).
3. L. D. Akulenko, G. V. Kostin, and S. V. Nesterov, “Numerical and Analytical Methods of Investigations of Free Oscillations of Nonuniform Rods,” Izv. Ross. Akad. Nauk: Mekh. Tverd. Tela, No. 5, 180–191 (1995).
4. F. L. Chernous’ko, “Decomposition and Suboptimal Control in Dynamic Systems,” Prikl. Mat. Mekh. 54(6), 883–893 (1990).
5. L. D. Akulenko, Asymptotic Methods of Optimal Control (Nauka, Moscow, 1987) [in Russian].