[Wu, Xia;Zhang, Jialu] Xiangnan Univ, Coll Math & Finance, Chenzhou 423000, Hunan, Peoples R China.^[Liu, Xiaoling] Xiangnan Univ, Coll Software & Commun Engn, Chenzhou 423000, Hunan, Peoples R China.^[Zhou, Li] Hunan Agr Univ, Coll Sci, Changsha 410128, Hunan, Peoples R China.