title: Expanding a tensor by another one with different dimensions in TensorFlow
body: <p>Let's say I have a tensor with shape <code>[a,b]</code> and another one with shape <code>[a,c]</code>, where <code>c&lt;b</code>. I want to merge both to a tensor with the dimensions <code>[a, b+c]</code>. How would one accomplish this in TensorFlow?</p>
  
  <p>Simply using <code>tf.concat</code> won't work in this case because it expects that all dimensions, except 0, to be equal:</p>
  
  <p><code>All dimensions except 0 must match. Input 1 has shape [a b] and doesn't match input 0 with shape [a c]</code> </p>