Department of Mathematics, Tufts University School of Arts and Sciences, Medford, MA, USA.|Department of Medicine, Center for Computational Biology and Bioinformatics, University of California San Diego, La Jolla, CA, USA.|Department of Medicine, Center for Computational Biology and Bioinformatics, University of California San Diego, La Jolla, CA, USA.|Department of Medicine, University of California San Diego, La Jolla, CA, USA.|Department of Medicine, Center for Computational Biology and Bioinformatics, University of California San Diego, La Jolla, CA, USA.