ZHU Hui-ming1, LI Rong1 , ZENG Zhao-fa2 ,YU Ke-ming3
(1. College of Business Administration, Hunan Univ, Changsha, Hunan410082, China;2. College of Finance and Statistics, Hunan Univ, Changsha, Hunan410079, China;3. Department of Mathematical Science, Brunel Univ, London UB83PH, UK)