Affiliation: | 1. Mathematical Department, Zhejiang Normal University, Zhejiang 321004, PR China;2. School of Mathematical Science, Peking University, Beijing 100871, PR China;1. Department of Mathematics, Shanghai University, Shanghai 200444, PR China;2. Department of Mathematics, Shanghai Normal University, Shanghai 200234, PR China;3. Center for Applied Mathematics and Theoretical Physics, University of Maribor, SI-2000 Maribor, Slovenia;4. Faculty of Natural Science and Mathematics, University of Maribor, SI-2000 Maribor, Slovenia |