任意上下幅值方波的傅里叶展开与合成。可以任意设置方波上下幅值和谐波级次，观察保留不同谐波级次对合成方波的影响，以及吉布斯现象。(Fourier expansion and synthesis of arbitrary upper and lower amplitude square waves. The influence of different harmonic levels on the synthetic square wave and the Gibbs phenomenon can be observed.)