Wuhan Univ Sci & Engn, Dept Math & Phys, Wuhan 430073, Peoples R China.
Chinese Acad Sci, Wuhan Inst Phys & Math, Wuhan 430071, Peoples R China.
Henan Vocat Coll Econ & Trade, Zhengzhou 450053, Peoples R China.
Cent China Normal Univ, Dept Math, Wuhan 430079, Peoples R China.
[Xia, Hongqiang] Wuhan Univ Sci & Engn, Dept Math & Phys, 1 Fangzhi Rd, Wuhan 430073, Peoples R China.