1. Department of Mathematics and Physics, Mianyang Normal University, Mianyang 621000, China
2. Department of Mathematics and Statistics, Curtin University, Perth, WA 6102, Australia
3. School of Finance, Zhongnan University of Economics and Law, Wuhan 430073, China
4. School of Statistics and Mathematics, Zhongnan University of Economics and Law, Wuhan 430073, China