1. Institute of Mathematics, Southeast University, Nanjing, Jiangsu Province, People's Republic of China
2. Nanjing Center for Applied Mathematics, Nanjing, Jiangsu Province, People's Republic of China
3. Department of Mathematics, Taiyuan Normal University, Jinzhong, Shanxi Province, People's Republic of China
4. School of Business, Qingdao University, Qingdao, Shandong Province, People's Republic of China