title: understand use of nn.Identity() in model definition using torch
body: <p>I was understanding the CGAN model given <a href="https://github.com/hezhangsprinter/ID-CGAN/blob/master/IDCGAN/models2.lua" rel="nofollow noreferrer">here</a>. 
  The generative model has symmetric skip connections as it is explained in the paper <a href="https://arxiv.org/pdf/1701.05957.pdf" rel="nofollow noreferrer">here</a>. Hence, I understand the lines such as:</p>
  
  <pre><code> d2 = {d2_,e4} - nn.CAddTable(true)
  </code></pre>
  
  <p>However, instead of doing the same thing after the last deconv layer d6, the following thing is done:</p>
  
  <pre><code>d6 = d61 - nn.Identity()
  </code></pre>
  
  <p>Can someone please help me understand why <code>nn.Identity()</code> is used here?</p>