[1] Xiamen Univ, Sch Math Sci, Xiamen 361005, Peoples R China
[2] Shandong Univ Sci & Technol, Coll Math & Syst Sci, Qingdao 266590, Peoples R China
[3] Capital Normal Univ, Sch Math Sci, Beijing 100048, Peoples R China
[4] Beijing Ctr Math & Informat Interdisciplinary Sci, Beijing 100048, Peoples R China