1. Institute for Analysis and Scientific Computing, TU Wien, Wiedner Hauptstraße 8-10, 1040 Wien, Austria
2. Department of Applied Mathematics and Statistics, Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynská Dolina, 84248 Bratislava, Slovakia
3. Institut für Mathematik, Universität Paderborn, Warburger Straße 100, 33098 Paderborn, Germany