1 Dept. of Mathematics, Aalborg University, Fredrik Bajers Vej 7 G, 9220 Aalborg gst, Denmark
2Dept. of Mathematics & Computer Science, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
3Lomonosov University of Moscow Faculty of Computational Mathematics and Cybernetics Leninskie Gory, 119992 Moscow, Russia
4 Dept. of Mathematics, Aalborg University, Fredrik Bajers Vej 7 G, 9220 Aalborg gst, Denmark