[1] Tsinghua Univ, Sch Software, Beijing 100084, Peoples R China
[2] RIKEN, Inst Phys & Chem Res, Biomimet Control Ctr, Nagoya, Aichi 4630003, Japan
[3] Seoul Natl Univ, Sch Elect Engn, Seoul 151742, South Korea
[4] Tsinghua Univ, Dept Math Sci, Beijing 100084, Peoples R China