1. Department of Statistics, University of Oxford, Oxford OX1 3TG, United Kingdom.
2. Department of Statistics and Applied Probability, National University of Singapore, Singapore 117546, Singapore.
3. Molecular and Computational Biology Program, University of Southern California, Los Angeles, California 90089-1340.
4. MOE Key Laboratory of Bioinformatics and Bioinformatics Division, TNLIST/Department of Automation, Tsinghua University, Beijing, P.R. China.