1. Department of Mathematics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
2. Johann Radon Institute for Computational and Applied Mathematics, Altenbergerstraße 69, Linz, Austria
3. Institute of Analysis and Scientific Computing, University of Graz, Heinrichstraße, 368010, Graz, Austria
4. Institute for Analysis and Scientific Computing, Technical University of Vienna, Wiedner, Hauptstraße 8-10, 1040 Wien, Austria