1. School of Science, Dalian Nationalities University, Liaoning, Dalian 116600, China
2. School of Information and Computing Science, Beifang University of Nationality, Ningxia, Yinchuan 750021, China
3. Department of Mathematics, Liaoning Normal University, Liaoning, Dalian 116029, China
4. Institute of Applied Physics and Computational Mathematics, Beijing 100094, China