1. School of Mathematics and Statistics, Sichuan University of Science and Engineering, Zigong, Sichuan, 643000, China
2. South Sichuan Center for Applied Mathematics, Sichuan University of Science and Engineering, Zigong, Sichuan, 643000, China
3. Department of Normal Education, Meishan Vocational and Technical College, Meishan, Sichuan, 620010, China