1. School of Integrated Design Engineering, Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
2. Department of Mechanical Engineering, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
3. Department of Computer Science, School of Computing, Tokyo Institute of Technology, 4259 Nagatsutacho, Midori-ku, Yokohama 226-8501, Japan