title: How to concat a 2-d tensor with a 3-d tensor
body: <p>In AE-lstm, 
  here is a lstm out with shape <code>[batch, timestamp, diml]</code>(regarded as <code>[b, t, dl]</code>) and the aspect vector is <code>[batch, dima]</code> (regarded as <code>[b, da]</code>)</p>
  
  <blockquote>
    <p>How to concat two variables to make the shape be <code>[b, t, dl+da]</code>?</p>
  </blockquote>
  
  <p>It means that for every batch, concat the aspect vector to every timestamp row.</p>