title: What is frequency-domain entropy in FFT result and how to calculate it?
body: <p>I am a programmer but quit bad on math..  I recently read an article which mentioned frequency-domain entropy,he calculated that thing from a FFT power spectrum but didn't tell me how to do that. I cannot find enough information online to understand what it is . I'm appreciate for any helps..</p>
  
  <p>Here is part of article:
  <img src="https://i.stack.imgur.com/B3KxB.png" alt="enter image description here"></p>