说明：  基于MATLAB 6.x开发，通过鼠标点击拖拽可以画出带箭头的线段。
(ARROW may be called with a normal argument list or a property-based list. ARROW(Start,Stop,Length,BaseAngle,TipAngle,Width,Page,CrossDir) is the full normal argument list, where all but the Start and Stop points are optional. If you need to specify a later argument (e.g., Page) but want default values of earlier ones (e.g., TipAngle), pass an empty matrix for the earlier ones (e.g., TipAngle=[]).)