1. State Key Laboratory of Scientific/Engineering Computing, Institute of Computational Mathematics and Scientific/Engineering Computing; Academy of Mathematics and Systems Science, Chinese Academy of Sciences; P.O. Box 2719, Beijing 100190 P.R. China
2. School of Mathematical Sciences; University of Chinese Academy of Sciences; Beijing 100049 P.R. China
3. Department of Mathematics; East China Normal University; Shanghai 200241 P.R. China