title: Changing the origin of a plot
body: <p>I have a table of data with 3 columns, which I want to plot the third column in terms of the first two in a colorful 2D plot. For example for the following table i.e.</p>
  
  <pre><code>4.0 4.0 0.313660827978 
  4.0 5.0 0.365348418405 
  4.0 6.0 0.423733120134 
  5.0 4.0 0.365348418405 
  5.0 5.0 0.439599930621 
  5.0 6.0 0.525083754405 
  6.0 4.0 0.423733120134 
  6.0 5.0 0.525083754405 
  6.0 6.0 0.651536351379
  </code></pre>
  
  <p>I use the following code:</p>
  
  <pre><code>x,y,z = np.loadtxt('output_overlap.dat').T #Transposed for easier unpacking
  nrows, ncols = final_step_j-1, final_step_k-1
  grid = z.reshape((nrows, ncols))
  plt.imshow(grid, extent=(x.min(), x.max(), y.max(), y.min()),
             interpolation='nearest', 
             cmap='binary')
  fig1 = plt.gcf()
  plt.colorbar()
  plt.xlabel('m1')
  plt.ylabel('m2')
  plt.draw()
  fig1.savefig('test.pdf', dpi=100)
  close('all')
  </code></pre>
  
  <p>which gives me the following plot:
  <a href="https://dl.dropboxusercontent.com/u/31460244/test.png" rel="nofollow">https://dl.dropboxusercontent.com/u/31460244/test.png</a></p>
  
  <p>Which is correct. Now, my question is: how can I change the order of showing data in the Y axis? I would like to have the point (4,4) at the origin. </p>
  
  <p>I have tried changing </p>
  
  <pre><code>plt.imshow(grid, extent=(x.min(), x.max(), y.max(), y.min())
  </code></pre>
  
  <p>to:</p>
  
  <pre><code>plt.imshow(grid, extent=(x.min(), x.max(), y.min(), y.max())
  </code></pre>
  
  <p>It does change the numbers in the grid but not the actual data. This is not the solution. Anybody can give me a help here?</p>