[1] School of Mathematics and System Sciences, Shandong University, Ji'nan 250100 Institute of Information Science, Beijing Jiaotong University, Beijing 100044
[2] Institute of Information Science, Beijing Jiaotong University, Beijing 100044
[3] School of Mathematics and System Sciences, Shandong University, Ji'nan 250100
[4] School of Arts and Science, Shandong University of Finance,Ji'nan 250014