1. Department of Mathematics, Guangdong University of Petrochemical Technology, Maoming, People's Republic of China
2. Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing, People's Republic of China
3. School of Sciences, Guangdong University of Petrochemical Technology, Maoming, People's Republic of China
4. School of Control Science and Engineering, Shandong University, Jinan, People's Republic of China