矩形波函数，计算其频谱，幅度谱和相位谱，与理论值比较。-Rectangular wave function to calculate the frequency spectrum, amplitude spectrum and phase spectrum, compared with the theoretical value.

用matlab编程绘制矩形窗函数的幅频特性，窗函数形状的长度为10，20，50，100.-Programming using matlab draw rectangle window function of the amplitude-frequency characteristics, the shape of window function of length of 10,20,50,100.