Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, 565-0871, Japan.|Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, 565-0871, Japan. ino@ist.osaka-u.ac.jp.|Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, 565-0871, Japan. hagihara@ist.osaka-u.ac.jp.