1. State Key Laboratory of Scientific and Engineering Computing, Institute of Computational Mathematics and Scientific Engineering Computing, Academy of Mathematics and System Sciences, Academia Sinica, P.O. Box 2719, Beijing 100080, P. R. China
2. Institute of Applied Physics and Computational Mathematics, Beijing 100088, P. R. China
3. Department of Computer Science, Hong Kong Baptist University, Kowloon Tong, Hong Kong, P. R. China