1. Department of Systems Engineering and Engineering Management, The Chinese University of Hong Kong, New Territories, Hong Kong SAR, People's Republic of China
2. Department of Computer Science, The University of Hong Kong, Pok Fu Lam, Hong Kong SAR, People's Republic of China
3. Department of Mathematics, University of California, Davis, CA, USA
4. Departments of Computer Science and Mathematics, The Hong Kong University of Science and Technology, Kowloon, Hong Kong SAR, People's Republic of China