1. a Department of Mathematics and Information Science , Yantai University , Yantai, Shandong Province, 264005, P.R. China
2. b Institute of Automation , Qufu Normal University , Qufu, Shandong Province, 273165, P.R. China
3. d School of Electrical Engineering and Automation , Xuzhou Normal University , Xuzhou, Jiangsu Province, 221116, P.R. China
4. c School of Information Science and Engineering , Northeastern University , Shenyang, Liaoning Province, 110004, P.R. China