中文说明：
Matlab做的关于三角波，正弦波，方波的FFT算法，可以分析方波信号、三角波信号的频谱以及采样点数、采样频率对频谱分辨率的影响。
English Description：
The FFT algorithm of triangular wave, sine wave and square wave made by Matlab can analyze the spectrum of square wave signal and triangular wave signal, as well as the influence of sampling points and sampling frequency on spectrum resolution