On model-free adaptive control: the state of the art and perspective. Control Theory and Applications, 2006, 23(4): 586-592 (侯忠生. 无模型自适应控制的现状和展望. 控制理论与应用, 2006, 23(4): 586-592)Hou Zhongsheng. On model-free adaptive control: the state of the art and perspective...