Affiliation: | 1. College of Mathematics and Statistics, Chongqing University , Chongqing 400044, P.R. China;2. College of Mathematics and Computer Sciences, Yangtze Normal University , Fuling 408100, Chongqing, P.R. China miyongshen@163.com;4. College of Mathematics and Statistics, Chongqing University , Chongqing 400044, P.R. China;5. College of Mathematics and Computer Sciences, Yangtze Normal University , Fuling 408100, Chongqing, P.R. China |