1. Department of Mathematics & KLDAIP, Chongqing University of Arts and Sciences, Yongchuan, Chongqing 402160, China
2. College of Mathematics and Statistics, Chongqing Technology and Business University, Chongqing 400067, China
3. College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, Chongqing 400065, China