[1] Xihua Univ, Sch Comp & Software Engn, Chengdu 610039, Sichuan, Peoples R China
[2] Univ Elect Sci & Technol China, Sch Comp Sci & Engn, Chengdu 611731, Sichuan, Peoples R China
[3] Beijing Inst Technol, Sch Software, Beijing 100081, Peoples R China