title: Performance of index creation
body: <p>In trying to choose which indexing method to recommend, I tried to measeure the performance. However, the measurements confused me a lot. I ran this multiple times in different orders, but the measurements remain consistent.
  Here is how I measured the performance:</p>
  
  <pre><code>for N = [10000 15000 100000 150000]
      x =  round(rand(N,1)*5)-2;
      idx1 = x~=0;
      idx2 = abs(x)&gt;0;
  
      tic
      for t = 1:5000
          idx1 = x~=0;
      end
      toc
  
      tic
      for t = 1:5000
          idx2 = abs(x)&gt;0;
      end
      toc
  end
  </code></pre>
  
  <p>And this is the result:</p>
  
  <pre><code>Elapsed time is 0.203504 seconds.
  Elapsed time is 0.230439 seconds.
  
  Elapsed time is 0.319840 seconds.
  Elapsed time is 0.352562 seconds.
  
  Elapsed time is 2.118108 seconds. % This is the strange part
  Elapsed time is 0.434818 seconds.
  
  Elapsed time is 0.508882 seconds.
  Elapsed time is 0.550144 seconds.
  </code></pre>
  
  <p>I checked and for values around 100000 this also happens, even at 50000 the strange measurements occur.</p>
  
  <p>So my question is: Does anyone else experience this for a certain range, and what causes this? (Is it a bug?) </p>