1. Fraunhofer Institute for Industrial Mathematics; Fraunhofer-Platz 1 67663 Kaiserslautern Germany
2. Martin Luther University Halle-Wittenberg; Institute of Mathematics; 06099 Halle (Saale) Germany
3. TU Kaiserslautern; Department of Mathematics; Paul-Ehrlich-Straße 67663 Kaiserslautern Germany