Dong Yucheng was born in 1979. Now he is a candidate of Ph.D. in Management School, Xi'an Jiaotong University. His main research interests include group decision making, online algorithm. E-mail: ycdong@mail.xj tu.edu.cn. Xu Yinfeng was born in 1962. He is a professor and doctor supervisor of Management School, Xi'an Jiaotong University. His main research interests include theoretical computer science, approximation algorithm and online algorithm. E-mail: yfxu@mail.xjtu.edu.cn. Ding Lill was born in 1978. Now she is a candidate of Ph.D. in management school, Xi'an Jiaotong University. His main research interests include online algorithm, risk management. E-mail: llding@mail.xjtu.edu.cn.