1. Institut für Mathematik, Humboldt University of Berlin, 10099 Berlin, Germany.
2. Norwegian University of Science and Technology, Department of Mathematical Sciences, NO-7041 Trondheim, Norway.
3. Interdisciplinary Center for Scientific Computing, Heidelberg University, 69120 Heidelberg, Germany.
4. University of Alcalá, Department of Physics and Mathematics, 28801 Alcalá DE Henares, Spain.