[1] Beijing Normal Univ, Sch Math Sci, Lab Math & Complex Syst, Beijing 100875, Peoples R China
[2] East China Normal Univ, Dept Math, Shanghai Key Lab PMMP, Dong Chuan Rd 500, Shanghai 200241, Peoples R China
[3] Univ Picardie, Fac Math & LAMFA, CNRS, UMR 7352, 33 Rue St Leu, F-80039 Amiens 1, France