GMD-German National Research Center for Information Technology, Institute for Algorithms and Scientific Computing (SCAI), Schloss Birlinghoven, D-53754 Sankt Augustin, Germany. Robert.Kueffner@gmd.de|GMD-German National Research Center for Information Technology, Institute for Algorithms and Scientific Computing (SCAI), Schloss Birlinghoven, D-53754 Sankt Augustin, Germany. Robert.Kueffner@gmd.de|GMD-German National Research Center for Information Technology, Institute for Algorithms and Scientific Computing (SCAI), Schloss Birlinghoven, D-53754 Sankt Augustin, Germany. Robert.Kueffner@gmd.de