说明：  离散傅立叶变换DFT源程序，包括时域离散化，求W算子表，原信号的时域描述和离散频域描述。以及快速傅立叶变换FFT源程序，里面有蝶形算法的循环步骤。适合初学者
(Discrete Fourier Transform DFT source, including the time-domain discretization, find the W operator table, the original description of the time-domain signal and discrete frequency domain description. And a Fast Fourier Transform FFT source, there are the circulating step of the butterfly algorithm. For beginners)