title: NaN or Inf arrays preallocation
body: <p>Array indexing can be used for <a href="http://www.gnu.org/software/octave/doc/interpreter/Advanced-Indexing.html#Advanced-Indexing" rel="nofollow">efficient array preallocation</a>. For instance</p>
  
  <pre><code>2(ones(1, 3))
  ans =
  
     2   2   2
  </code></pre>
  
  <p>but this does not work with NaN or Inf</p>
  
  <pre><code>NaN(ones(1, 3))
  ans = NaN
  </code></pre>
  
  <p>Why ?</p>