Shujun Fu1,2, Qiuqi Ruan2, Wenqia Wang1 and Jingnian Chen3
1School of Mathematics and System Sciences
Shandong University
Jinan, 250100, China
E-mail: shujunfu@163.com
2Institute of Information Science
Beijing Jiaotong University
Beijing, 100044, China
3School of Arts and Science
Shandong University of Finance
Jinan, 250014, China