说明：  本代码通过MATLAB绘制了绕射波的时距曲线，可直观地观察出绕射波时距曲线与直达波时距曲线的差别
(This code draws the time-distance curve of the diffracted wave through MATLAB, and can observe the difference between the time-distance curve of the diffracted wave and the time-distance curve of the direct wave intuitively.)