fftw库，可以在windows下和Linux下同时使用，值得下载-fftw library, under windows and can be used under Linux, it is worth downloading

代码举例了3中函数的fft变换。需要用到fftw库文件，可以自己到fftw官方下载-Examples of code in the function fft transform 3. Need to use fftw library file, you can download your own to fftw official