说明：  FFT（Fast Fourier Transformation）是离散傅氏变换（DFT）的快速算法。即为快速傅氏变换。它是根据离散傅氏变换的奇、偶、虚、实等特性，对离散傅立叶变换的算法进行改进获得的。
(FFT (Fast Fourier Transformation) is a fast algorithm for discrete Fourier transform (DFT). Is the fast Fourier transform. It is based on the discrete Fourier transform of the odd, even, virtual, real and other characteristics of the discrete Fourier transform algorithm to improve the obtained.)