1. School of Science, Southwest University of Science and Technology, Mianyang, People's Republic of China
2. School of Mathematical Sciences, Sichuan Normal University, Chengdu, People's Republic of China
3. Visual Computing and Virtual Reality Key Laboratory of Sichuan Province, Sichuan Normal University, Chengdu, People's Republic of China
4. School of Mathematics, Chengdu Normal University, Chengdu, People's Republic of China