1. School of Mathematical Sciences, University of Chinese Academy of Science, Beijing, People’s Republic of China and Institute of Applied Mathematics, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing, People’s Republic of China.
2. Institute of Applied Mathematics, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing, People’s Republic of China and School of Mathematical Sciences, University of Chinese Academy of Science, Beijing, People’s Republic of China.
3. Institute of Applied Mathematics, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing, People’s Republic of China.
4. Department of Mathematics, Beijing University of Technology, Beijing, People’s Republic of China.