1. School of Statistics and Mathematics, Shandong University of Finance and Economics, Jinan 250014, China
2. School of Science, Guangxi University of Science and Technology, Liuzhou 545006, China
3. Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing 100190, China
4. Department of Mathematical and Statistical Sciences, University of Alberta, Edmonton, AB T6G 2G1, Canada
5. Zhongtai Securities Institute for Financial Studies, Shandong University, Jinan 250100, China