Affiliation: | 1. Academy of Mathematics and Systems Science, Academia Sinica , Beijing , People's Republic of China;2. School of Computational and Applied Mathematics , University of the Witwatersrand , Johannesburg , South Africa bzguo@iss.ac.cn;4. Department of Mathematics , Beijing Institute of Technology , Beijing , People's Republic of China;5. School of Computational and Applied Mathematics , University of the Witwatersrand , Johannesburg , South Africa |