1. Postdoctoral Programme of Management Science and Engineering, Shandong Normal University, Jinan, Shandong, China
2. School of Mathematics and Statistics, Shandong Normal University, Jinan, Shandong, China
3. School of Management Science and Engineering, Shandong Normal University, Jinan, Shandong, China
4. School of Information Science and Engineering, Shandong Normal University, Jinan, Shandong, China