1. Department of Mathematics, School of Information, Renmin University of China, Beijing, People’s Republic of China.
2. Department of Mathematics and Statistics, Georgetown University, Washington, DC, USA.
3. Department of Mathematics, Fu Jen Catholic University, Taipei, Taiwan, Republic of China.
4. Hubei Key Laboratory of Applied Mathematics, School of Mathematics and Statistics, Hubei University, Wuhan, People’s Republic of China.
5. Laboratory of Mathematics and Complex Systems, Ministry of Education, School of Mathematical Sciences, Beijing Normal University, Beijing, People’s Republic of China.