1. School of Mathematics and Information Science, Guangzhou University, Guangzhou 510006, China
2. Key Laboratory of Mathematics and Interdisciplinary Sciences of Guangdong Higher Education Institutes, Guangzhou University, Guangzhou 510006, China
3. Cisco School of Informatics, Guangdong University of Foreign Studies, Guangzhou 510420, China
4. Department of Mathematics and Physics, Shanghai Dianji University, Shanghai 201306, China
5. School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China