1. Faculty of Life Sciences, A. V. Hill Building, University of Manchester, Manchester M13 9PT, UK.
2. Department of Industrial and Operations Engineering, University of Michigan, Ann Arbor, MI 48109, USA.
3. Center for Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI 48109, USA.
4. Department of Mathematics, University of Michigan, Ann Arbor, MI 48109, USA.