1. Graduate School of Engineering Science, Osaka University, 1-2 Machikaneyama-cho, Toyonaka-shi 560-0043, Japan
2. Graduate School of Engineering, Kyoto University, Katsura Campus, Nishikyo-ku, Kyoto 615-8540, Japan
3. Principles of Informatics Research Division, National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku 101-8430, Japan