School of Mathematics and Statistics, Huazhong University of Science and Technology, Wuhan, 430074, China
LAMFA, Université Picardie Jules Verne, Amiens, 80039, France
Email: bwei_wang@yahoo.com.cn
School of Mathematics and Statistics, Huazhong University of Science and Technology, Wuhan, 430074, China
LAMFA, Université Picardie Jules Verne, Amiens, 80039, France
Email: bwei_wang@yahoo.com.cn