1. Friedrich-Schiller-Universität Jena, School of Mathematics and Computer Science, Institute of Applied Mathematics, 07737 Jena, Germany
2. Department of Electrical Engineering, Tokyo University of Science, Yamaguchi, Sanyo-Onoda, Yamaguchi 756–0884, Japan
3. Department of Information Sciences, Tokyo University of Science, Noda City, Chiba 278–8510, Japan