如果在matlab中已经打开一一个figure，输入t之后就可以选取想要的点，按y即可确定，接着输入下一个点。按q推出程序。所有点的坐标保存在x_all和y_all中。(If you have already opened a figure in MATLAB, you can select the desired point after you enter t, press y to determine, and then enter the next point. Press Q to launch the program. The coordinates of all points are stored in x_all and y_all.)