1. College of Mathematics and Statistics, Changsha University of Science and Technology, Changsha, People's Republic of China
2. College of Statistics and Mathematics, Zhongnan University of Economics and Law, Wuhan, People's Republic of China
3. College of Economics and Trade, Hunan University of Technology and Business, Changsha, People's Republic of China
4. College of Mathematics and Statistics, Jishou University, Jishou, People's Republic of China