[1] Southwest Jiaotong Univ, Sch Math, Chengdu 611756, Sichuan, Peoples R China
[2] Univ Elect Sci & Technol China, Sch Math Sci, Res Ctr Image & Vis Comp, Chengdu 611731, Sichuan, Peoples R China
[3] Northwestern Polytech Univ, Sch Math & Stat, Xian 710072, Shaanxi, Peoples R China
[4] RIKEN, Ctr Adv Intelligence Project, Tokyo 1030027, Japan