title: Why do numpy cov diagonal elements and var functions have different values?
body: <pre><code>In [127]: x = np.arange(2)
  
  In [128]: np.cov(x,x)
  Out[128]:
  array([[ 0.5,  0.5],
         [ 0.5,  0.5]])
  
  In [129]: x.var()
  Out[129]: 0.25
  </code></pre>
  
  <p>Why is this the behavior? I believe that covariance matrix diagonal elements should be the variance of the series. </p>