1. School of Economics, Southwest University of Finance and Economics, Chengdu, People's Republic of China
2. Department of Applied Mathematics, Nanjing Forestry University, Nanjing, People's Republic of China
3. School of Mathematics (Zhuhai), Sun Yat-Sen University, Zhuhai, People's Republic of China
4. Department of Mathematics, Zhejiang Normal University, Jinhua, People's Republic of China