title: power spectrum by numpy.fft.fft
body: <p>The figure I plot via the code below is just a peak around ZERO, no matter how I change the data. My data is just one column which records every timing points of some kind of signal. Is the <code>time_step</code> a value I should define according to the interval of two neighbouring points in my data?  </p>
  
  <pre><code>data=np.loadtxt("timesequence",delimiter=",",usecols=(0,),unpack=True)
  
  ps = np.abs(np.fft.fft(data))**2
  time_step = 1
  
  freqs = np.fft.fftfreq(data.size, time_step)
  idx   = np.argsort(freqs)
  
  pl.plot(freqs[idx], ps[idx])
  pl.show()
  </code></pre>