1. Department of Applied Mathematics, Xi'an University of Technology, Xi'an, China
2. Department of Finance and Statistics, Xi'an Polytechnic University, Xi'an, China
3. Faculty of Science, Kunming University of Science and Technology, Kunming, China
4. School of Software Engineering, Beijing Jiaotong University, Beijing, China
5. College of Science, Xi'an Shiyou University, Xi'an, China