title: Integration in numpy array with positive area only
body: <p>I want to be able to compute following integral using numpys trapz function</p>
  
  <pre><code>numpy.trapz([-1, 1]) # returns 0
  </code></pre>
  
  <p>But I don't want to allow negative areas. Is there an efficient way to do this or do I have to look for the minimum point and transform the array by hand?</p>
  
  <p>Does <code>numpy.trapz(numpy.abs([-1, 1]))</code> make sense?</p>