title: how to do spectrum analyse with FFTW?
body: <p>I would like to better understand FFTW's API. FFTW is a library for computing the discrete Fourier transform (DFT) in one or more dimensions.</p>
  
  <p>Now, assume I have a sinus waveform  x=30*sin(2*M_PI*f*i*T), where f is the frequency (for example f=1000Hz).
   If I use FFTW's function to analyse my waveform, I expect to get one frequency f=1000Hz.</p>
  
  <p>My question is how can I do this in c++ using FFTW Library?
  Any help would be appreciated.</p>