title: Python : 2d contour plot from 3 lists : x, y and rho?
body: <p>I have a simple problem in python and matplotlib.
  I have 3 lists : x, y and rho with rho[i] a density at the point x[i], y[i].
  All values of x and y are between -1. and 1. but they are not in a specific order.</p>
  
  <p>How to make a contour plot (like with imshow) of the density rho (interpolated at the points x, y).</p>
  
  <p>Thank you very much.</p>
  
  <p>EDIT : I work with large arrays : x, y and rho have between 10,000 and 1,000,000 elements</p>