title: How to add a new dimension to a PyTorch tensor?
body: <p>In NumPy, I would do</p>
  <pre class="lang-py prettyprint-override"><code>a = np.zeros((4, 5, 6))
  a = a[:, :, np.newaxis, :]
  assert a.shape == (4, 5, 1, 6)
  </code></pre>
  <p>How to do the same in PyTorch?</p>