title: Python: 2D color map with imshow
body: <p>I am trying to represent a function of two variable on a two dimensional graph using color.
  I came across this example <a href="http://glowingpython.blogspot.ca/2012/01/how-to-plot-two-variable-functions-with.html" rel="nofollow noreferrer">here</a>:</p>
  
  <pre><code>from numpy import exp,arange
  from pylab import meshgrid,cm,imshow,contour,clabel,colorbar,axis,title,show
  # the function that I'm going to plot
  def z_func(x,y):
   return (1-(x**2+y**3))*exp(-(x**2+y**2)/2)
  
  x = arange(-3.0,3.0,0.1)
  y = arange(-3.0,3.0,0.1)
  X,Y = meshgrid(x, y) # grid of point
  Z = z_func(X, Y) # evaluation of the function on the grid
  
  im = imshow(Z,cmap=cm.RdBu) # drawing the function
  # adding the Contour lines with labels
  cset = contour(Z,arange(-1,1.5,0.2),linewidths=2,cmap=cm.Set2)
  clabel(cset,inline=True,fmt='%1.1f',fontsize=10)
  colorbar(im) # adding the colobar on the right
  # latex fashion title
  title('$z=(1-x^2+y^3) e^{-(x^2+y^2)/2}$')
  show()
  </code></pre>
  
  <p>which produces <img src="https://i.stack.imgur.com/osm65.png" alt="enter image description here"></p>
  
  <p>However, the axis scales and limits do not correspond to the real x and y data(both of which are between -3 and 3). How to make them correspond to the actual data?</p>