1. Department of Electrical EngineeringDoshisha University1‐3 Tatara MiyakodaniKyotanabeKyoto610‐0321Japan
2. Science Solutions International Laboratory, Inc.2‐21‐7 Naka‐choMeguro‐kuTokyo153‐0065Japan
3. Information Initiative CenterHokkaido UniversityKita‐11 Nishi‐5Kita‐kuSapporo060‐0811Japan
4. Academic Center for Computing and Media StudiesKyoto UniversityYoshida‐HonmachiKyoto606‐8501Japan