1. School of Finance, Nanjing Audit University, Nanjing, China;
2. Jiangsu Key Laboratory of Financial Engineering, Nanjing Audit University, Nanjing, 211815, China;
3. School of Mathematical Science, University of Electronic Science and Technology of China, Chengdu, China;
4. Department of Mathematics, Nanjing University, Nanjing, P. R. China