1. School of Mathematics and Statistics, North China University of Water Resources and Electric Power, Zhengzhou, People's Republic of China
2. School of Mathematics and Information Technology, Yuncheng University, Yuncheng, People's Republic of China
3. Zhongtai Securities Institute for Financial Studies, Shandong University, Jinan, People's Republic of China
4. Shandong National Center for Applied Mathematics, Shandong Province Key Laboratory of Financial Risk, Shandong, People's Republic of China