title: Expand python matrix along extra dimension
body: <p>I have a 2 dimensional <code>3x3</code> array e.g.:  </p>
  
  <pre><code>(4,5,6
  
   8, 10, 12
  
   12,15,18 )
  </code></pre>
  
  <p>I would like to multiply this by a vector <code>(1,2,3)</code> so that I end up with a <code>3x3x3</code> array where along the third dimension all the elements of the original array are multiplied by 1, 2 or 3 respectively. How do it do this in python?  </p>