title: drawing bivariate gaussian distributions in matplotlib
body: <p>How can we plot (in python matplotlib) bivariate Gaussian Distributions , given their centers and covariance matrices as numpy arrays?</p>
  
  <p>Let's say that our parameters are as follows:</p>
  
  <pre><code>center1=np.array([3,3])
  center2=np.array([5,5])
  cov1=np.array([ [1.,.5], [.5,.1]])
  cov2=np.array([ [.2,.5], [.5,.2]])
  </code></pre>