title: Is there a built-in KL divergence loss function in TensorFlow?
body: <p>I have two tensors, <code>prob_a</code> and <code>prob_b</code> with shape <code>[None, 1000]</code>, and I want to compute the KL divergence from <code>prob_a</code> to <code>prob_b</code>. Is there a built-in function for this in TensorFlow?  I tried using <code>tf.contrib.distributions.kl(prob_a, prob_b)</code>, but it gives:</p>
  
  <blockquote>
    <p>NotImplementedError: No KL(dist_a || dist_b) registered for dist_a type Tensor and dist_b type Tensor</p>
  </blockquote>
  
  <p>If there is no built-in function, what would be a good workaround?</p>