1. Department of Applied Mathematics, Lobachevsky University, 603950 Nizhny Novgorod, Russia
2. Mathematical Center, Lobachevsky University, 603950 Nizhni Novgorod, Russia
3. Department of Computer Science, Oslo Metropolitan University, N-0130 Oslo, Norway
4. Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Straße 38, 01187 Dresden, Germany