说明：  此程序给出由三个不同频率的正弦所组成信号的联合时－频分布。该图是三维图形的二维投影，在该图中，一个轴是时间，一个轴是频率。由该图可清楚地看出信号的时间－频率关系。
(This program shows three different frequency sinusoidal signal composed of joint time- frequency distribution. The plan is two-dimensional projection three-dimensional graphics in the figure, one axis is time, an axis is frequency. By the diagram is clear that the signal of the time- frequency relation.)