1. Department of Computer, Qinghai Normal University, Xining, Qinghai, China
2. School of Mathematics and Statistics, Qinghai Normal University, Xining, Qinghai, China
3. Academy of Plateau Science and Sustainability, People’s Government of Qinghai Province and Beijing Normal University, Xining, Qinghai, China
4. Department of Basic Research, Qinghai University, Xining, Qinghai, China