[Yu, Ying;Jia, Jinglan] Cent China Normal Univ, Sch Math & Stat, Wuhan, Hubei, Peoples R China.^[Li, Deying] Renmin Univ China, Sch Informat, Beijing, Peoples R China.^[Zhu, Yuqing] Calif State Univ Los Angeles, Dept Comp Sci, Los Angeles, CA 90032 USA.