title: numpy.fft() what is the return value amplitude + phase shift OR angle?
body: <p>The np.fft.fft() returns a complex array .... what is the meaning of the complex number ?
  I suppose the real part is the amplitude !
  The imaginary part is phase-shift ? phase-angle ? Or something else !</p>
  
  <p>I figured out the position in the array represent the frequency.</p>