Affiliation: | (1) Department of Mathematics, Chongqing Normal University, Chongqing, China;(2) Present address: Department of Applied Mathematics, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong;(3) Department of Applied Mathematics, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong;(4) Institute of Systems Science, Chinese Academy of Sciences, Beijing, China |