1. College of Economics and Management, China Three Gorges University, Yichang 443002, China
2. Economics and Management Department, Guangxi Minzu Normal University, Chongzuo 532200, China
3. College of Mathematics and Information Sciences, Guangxi University, Nanning 530004, China
4. Department of Mathematics and Physics, Liuzhou Institute of Technology, Liuzhou 545616, China