title: Adding a number to each column of a matrix
body: <p>I have a matrix</p>
  
  <pre><code>A = [[  1.  2.  3.]
       [  4.  5.  6.]]
  </code></pre>
  
  <p>and a vector</p>
  
  <pre><code>b = [ 5.  10.  15.]
  </code></pre>
  
  <p>I want to add each column of A (<code>A[:,i]</code>) to <code>b[i]</code>, i.e.</p>
  
  <pre><code>[[  6.  12.  18.]
   [  9.  15.  21.]]
  </code></pre>
  
  <p>an easy way to do it would be</p>
  
  <pre><code>A = tf.constant([[1., 2, 3],[1, 2, 3]])
  b = tf.constant([[5, 10, 15.]])
  e = tf.ones((2,1))
  a + tf.matmul( e, b ) # outer product "repmat"
  </code></pre>
  
  <p>But it seems terribly wasteful to do this and have to construct an entire auxiliary matrix which we will eventually throw out. Is there a more idomatic way of doing this without writing my own op?</p>