1. School of Mathematics and Economics, Hubei University of Education, Second Gaoxin Road, Wuhan 430205, Hubei, China
2. Faculty of Mathematics and Statistics, Hubei Key Laboratory of Applied Mathematics, Hubei University, 430062 Wuhan, P. R. China
3. Faculty of Computer Science and Information Engineering, Hubei University, 430062 Wuhan, P. R. China