title: matplotlib pcolor axes scale
body: <p>I have used pcolor to plot a heatmap:</p>
  
  <pre><code>df = df.groupby(['d','f'])['beta'].sum()
  beta_df = df.unstack('f')
  plt.pcolor(beta_df)
  </code></pre>
  
  <p>beta_df is size 35x35, beginning thus:</p>
  
  <pre><code>f             0.05      0.06      0.07      0.08      0.09      0.10  ...
  d                                                                      
  0.050000  0.993125  0.993264  0.991511  0.995148  1.000422  1.003847   
  0.105714  0.997931  0.998003  0.997459  1.000743  1.005858  1.001873 
  ...
  </code></pre>
  
  <p>However, the axes contain integers from 0 to 35 instead of the values of f and d. How to fix it?</p>