title: Renormalize weight matrix using TensorFlow
body: <p>I'd like to add a max norm constraint to several of the weight matrices in my TensorFlow graph, ala Torch's <a href="http://torch7.readthedocs.org/en/rtd/maths/#torchrenormres-x-p-dim-maxnorm" rel="noreferrer"><code>renorm</code></a> method.</p>
  
  <p>If the L2 norm of any neuron's weight matrix exceeds <code>max_norm</code>, I'd like to scale its weights down so that their L2 norm is exactly <code>max_norm</code>.</p>
  
  <p>What's the best way to express this using TensorFlow?</p>