1. Hunan Provincial Key Laboratory of Intelligent Computing and Language Information Processing, and the College of Information Science and Engineering, Hunan Normal University, Changsha, China
2. School of Mathematical Sciences, Anhui University, Hefei, China
3. School of Economics and Management, Southwest Jiaotong University, Chengdu, China
4. School of Information Science and Technology, Nantong University, Nantong, China