1. Department of Mathematical Information Technology, University of Jyväskylä, P. O. Box 35 (Agora), FI-40014 University of Jyväskylä, Finland
2. Numerola Oy, P. O. Box 126, FI-40101 Jyväskylä, Finland
3. Institute for Computational and Mathematical Engineering, Durand Building, Stanford University, Stanford, CA 94305, USA