[1] Beijing Univ Technol, Coll Appl Sci, Beijing 100124, Peoples R China
[2] Beijing Univ Technol, Beijing Inst Sci & Engn Comp, Beijing 100124, Peoples R China
[3] City Univ Hong Kong, Dept Math, Hong Kong, Hong Kong, Peoples R China
[4] Hong Kong Baptist Univ, Dept Math, Hong Kong, Hong Kong, Peoples R China