title: covariance of two vectors in matlab
body: <p>I am trying to compute the covariance between two vectors in matlab:</p>
  
  <pre><code>x = [1:10]
  y = [21:30]
  cov(x,y)
  </code></pre>
  
  <p>This returns the matrix of covariance and variance. I just want 1 number: the covariance between the two vectors.  How does one get this in matlab?</p>