title: use negative loss in tensorflow
body: <p>I am implementing a reinforcement agent that takes actions based on classes.
  so it can take action 1 or 2 or 3 or 4.</p>
  
  <p>So my question is can I use negative loss in tensorflow to stop it from outputting an action.</p>
  
  <p>Example:
  Let's say the agent outputs action 1 I want to very strongly dissuade it from taking action 1 in that situation again.  but there is not a known action that it should have taken instead.  So I can't just choose a different action to make it learn that.</p>
  
  <p>So my question is:
  does tensorflow gradient computation handle negative values for loss.
  And if it does will it work the way I describe?</p>