Simulation of Biological Systems, Center for Bioinformatics, Eberhard Karls University Tübingen, Tübingen, Germany. toussaint@informatik.uni-tuebingen.de|Simulation of Biological Systems, Center for Bioinformatics, Eberhard Karls University Tübingen, Tübingen, Germany. toussaint@informatik.uni-tuebingen.de|Simulation of Biological Systems, Center for Bioinformatics, Eberhard Karls University Tübingen, Tübingen, Germany. toussaint@informatik.uni-tuebingen.de