Fraunhofer Institute for Algorithms and Scientific Computing, Schloss Birlinghoven, D-53754 Sankt Augustin, Germany. ingolf.sommer@gmd.de|Fraunhofer Institute for Algorithms and Scientific Computing, Schloss Birlinghoven, D-53754 Sankt Augustin, Germany. ingolf.sommer@gmd.de|Fraunhofer Institute for Algorithms and Scientific Computing, Schloss Birlinghoven, D-53754 Sankt Augustin, Germany. ingolf.sommer@gmd.de|Fraunhofer Institute for Algorithms and Scientific Computing, Schloss Birlinghoven, D-53754 Sankt Augustin, Germany. ingolf.sommer@gmd.de|Fraunhofer Institute for Algorithms and Scientific Computing, Schloss Birlinghoven, D-53754 Sankt Augustin, Germany. ingolf.sommer@gmd.de