title: Parfor in MATLAB Problem
body: <p>Why can't I use the <code>parfor</code> in this piece of code?</p>
  
  <pre><code>parfor i=1:r
  
      for j=1:N/r
  
          xr(j + (N/r) * (i-1)) = x(i + r * (j-1));
  
      end
  
  end
  </code></pre>
  
  <p>This is the error:</p>
  
  <blockquote>
    <p>Error: The variable xr in a parfor cannot be classified.
     See Parallel for Loops in MATLAB, "Overview".</p>
  </blockquote>