1. RCSDS, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing 100190, China.
2. Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088, China.
3. Department of Mathematics, Computational Foundry, Swansea University, Swansea SA1 8EN, UK.
4. Corresponding author. School of Statistics and Mathematics, Chongqing University, Chongqing 400044, China.