1. Université de Lille, CNRS, UMR 8524 - Laboratoire Paul Painlevé, F-59000 Lille, France
2. Università degli Studi di Padova, Dipartimento di Matematica “Tullio Levi-Civita”, Via Trieste 63, 35121–Padova, Italy
3. Dept. of Computer Science and Engineering, University of Minnesota, Mississippi National River and Recreation Area, Minneapolis, MN 55455, USA