title: Pytorch how to stack tensor like for loop
body: <p>I want to concat tensor generated in for loop, and get 2dTensor.<br>
  standard python, like below.</p>
  
  <pre><code>li = []
  for i in range(0, len(items)):
      # calc something
      li.append(calc_result)
  </code></pre>
  
  <p>In my case, in for loop, generate <code>torch.Size([768])</code> Tensor, and I want to get <code>torch.Size([len(item),768])</code> Tensor.<br>
  How to do this?</p>