1. Department of Common Course Teaching, Anhui Xinhua University, Hefei 230088, Anhui, P. R. China
2. Department of Mathematics and Physics, Hefei University, Hefei 230601, Anhui, P. R. China
3. Business School, Sichuan University, Chengdu 610064, Sichuan, P. R. China
4. Department of Computer and Information Science, Faculty of Science and Technology, University of Macau, Macau
5. School of Computer Science and Technology, Anhui University, Hefei 230601, Anhui, P. R. China
6. Department of Mathematics and Computer Science, University of Münster, Einsteinstr. 62, 48149, Münster, Germany