title: Keras: Difference between Kernel and Activity regularizers
body: <p>I have noticed that <em>weight_regularizer</em> is no more available in Keras and that, in its place, there are <em>activity</em> and <em>kernel</em> regularizer. 
  I would like to know:</p>
  
  <ul>
  <li>What are the main differences between <em>kernel</em> and <em>activity</em> regularizers?</li>
  <li>Could I use <em>activity_regularizer</em> in place of <em>weight_regularizer</em>?</li>
  </ul>