National Laboratory of Pattern Recognition, Institute of Automation, Chinese Academy of Sciences, Beijing 100080, P R China. qhcui@nlpr.ia.ac.cn|National Laboratory of Pattern Recognition, Institute of Automation, Chinese Academy of Sciences, Beijing 100080, P R China. qhcui@nlpr.ia.ac.cn|National Laboratory of Pattern Recognition, Institute of Automation, Chinese Academy of Sciences, Beijing 100080, P R China. qhcui@nlpr.ia.ac.cn|National Laboratory of Pattern Recognition, Institute of Automation, Chinese Academy of Sciences, Beijing 100080, P R China. qhcui@nlpr.ia.ac.cn