1. School of Statistics and Mathematics, Nanjing Audit University, Nanjing 200815, China
2. Jiangsu Key Laboratory of Financial Engineering (Nanjing Audit University), Nanjing 211815, China
3. Department of Financial Engineering, Ningbo University, Ningbo 315211, China
4. School of Economics, Hangzhou Dianzi University, Hangzhou 310018, China