title: y axis of heat map not inverting in Python
body: <p>I'm generating 4 heat maps using subplots and want the y-axis inverted. I'm using <code>ax[i].invert_yaxis()</code> but it doesn't seem to be working. An example of the code is below:</p>
  
  <pre><code>everything = [data_y_axis, data_length, data_roundness, data_y_SDev]
  legend = ['title1', 'title2', 'title3', 'title4']
  
  fig, ax = plt.subplots(nrows = 1, ncols = 4, sharex = False, sharey = True, figsize = (13,3))
  
  ax = ax.flatten()
  
  for i, v in enumerate(everything):
  
      heatmap = ax[i].pcolor(v, cmap=plt.cm.Blues)
  
      ax[i].invert_yaxis()
      ax[i].xaxis.tick_top()
      ax[i].set_xticks(np.arange(v.shape[1])+0.5, minor=False)
      ax[i].set_xticklabels(column_labels, minor=False)
      ax[i].set_yticks(np.arange(v.shape[0])+0.5, minor=False)
      ax[i].set_yticklabels(row_labels, minor=False, fontproperties = titlefont)
      ax[i].set_xticklabels(column_labels, minor=False, fontproperties = titlefont)
  
      cb = fig.colorbar(heatmap, orientation='horizontal', pad=0.02, ax = ax[i])
      cb.set_label(label = legend[i], fontproperties = titlefont)
      cb.outline.set_linewidth(2)
  </code></pre>
  
  <p>The items in <code>everything</code> are just np.arrays, all of which have the same shape of (4, 6).</p>
  
  <p>It's currently producing maps like this:<a href="https://i.stack.imgur.com/wJg78.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wJg78.png" alt="enter image description here"></a> and should look like this: <a href="https://i.stack.imgur.com/08URE.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/08URE.png" alt="enter image description here"></a>.</p>
  
  <p>Have I done something obviously wrong?</p>