1. School of Mathematical Sciences, University of Electronic Science and Technology of China, Chengdu, Sichuan, China
2. Department of Civil, Geological and Mining Engineering, Polytechnique Montréal, Montreal, QC, Canada
3. School of Mathematics, Southwest Jiaotong University, Chengdu, Sichuan, China
4. School of Navigation, Wuhan University of Technology, Wuhan, China