[Wei, Jiangyong] Zhongnan Univ Econ & Law, Sch Math & Stat, Wuhan 430073, Hubei, Peoples R China.^[Hu, Xiaohua] Cent China Normal Univ, Sch Comp, Wuhan 430079, Hubei, Peoples R China.^[Zou, Xiufen] Wuhan Univ, Sch Math & Stat, Wuhan 430072, Hubei, Peoples R China.^[Tian, Tianhai] Monash Univ, Sch Math Sci, Melbourne, Vic 3800, Australia.