1. LSEC, ICMSEC, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing 100190, P. R. China
2. School of Mathematical Sciences, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
3. School of Mathematics and Computational Science & Hunan Key Laboratory for Computation and Simulation in Science and Engineering, Xiangtan University, Hunan 411105, P. R. China