Seminar for Applied Mathematics, ETH Zürich, Zürich, Switzerland.|Department of Biosystems Science and Engineering and SIB Swiss Institute of Bioinformatics, ETH Zürich, Zürich, Switzerland.|Department of Biosystems Science and Engineering and SIB Swiss Institute of Bioinformatics, ETH Zürich, Zürich, Switzerland.|Seminar for Applied Mathematics, ETH Zürich, Zürich, Switzerland.