Institute of Computational Biology, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany and Department of Mathematics, Technische Universität München, Boltzmannstraße 3, 85747 Garching, Germany Institute of Computational Biology, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany and Department of Mathematics, Technische Universität München, Boltzmannstraße 3, 85747 Garching, Germany.