1. The MOE-LCSM, School of Mathematics and Statistics, Hunan Normal University , Changsha, Hunan 410081 , China
2. Journal House, Hunan Normal University , Changsha, Hunan 410081 , China
3. The Key Laboratory of Control and Optimization of Complex Systems, College of Hunan Province, Hunan Normal University , Changsha 410081 , China
4. Dpto. Ecuaciones Diferenciales y Análisis Numérico, Facultad de Matemáticas, Universidad de Sevilla , c/ Tarfia s/n, E-41012 Sevilla , Spain
5. Department of Mathematics, Wenzhou University , Wenzhou 325035, Zhejiang Province , P. R. China