1. Johann Radon Institute for Computational Mathematics, Austrian Academy of Sciences, A-4040 Linz, Austria.
2. Institute for Computational Mathematics, Johannes Kepler University Linz, A-4040 Linz, Austria.
3. Leibniz Universität Hannover, Institut für Angewandte Mathematik, 30167 Hannover, Germany, and Cluster of Excellence PhoenixD (Photonics, Optics, and Engineering - Innovation Across Disciplines), Leibniz Universität Hannover, Germany.