title: How do you concatenate symbols in mxnet
body: <p>I have 2 symbols in MXNet and would like to concatenate them. How can i do this:</p>
  
  <p>eg: <code>a = [100,200]</code>, <code>b = [300,400]</code>, Id like to get</p>
  
  <p><code>c = [100,200,300,400]</code></p>