1. Department of Mathematics, King’s College London, Strand, London WC2R 2LS, UK
2. Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade, University of Belgrade, Pregrevica, 118, 11080 Belgrade, Serbia
3. Institut für Theoretische Physik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany