1. Department of Finance and Research Center for Econophysics, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, P. R. China
2. Department of Mathematics, East China University of Science and Technology, Shanghai 200237, P. R. China
3. Department of Finance, Department of Mathematics and Research Center for Econophysics, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, P. R. China