title: Matplotlib: how to add xlabel, title to each subplot
body: <p>I'm trying to plot multiple heatmaps using the <code>plt.subplots</code>. An example I found is as follows:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  
  # Generate some data that where each slice has a different range
  # (The overall range is from 0 to 2)
  data = np.random.random((4,10,10))
  data *= np.array([0.5, 1.0, 1.5, 2.0])[:,None,None]
  
  # Plot each slice as an independent subplot
  fig, axes = plt.subplots(nrows=1, ncols=4,figsize=(12,3))
  i=0
  for dat, ax in zip(data, axes.flat):
      # The vmin and vmax arguments specify the color limits
      im = ax.imshow(dat, vmin=0, vmax=2,cmap='Reds')
      # ax.xlabel(str(i))
      # ax.ylabel(str(i))
      i += 1
  
  # Make an axis for the colorbar on the right side
  cax = fig.add_axes([0.95, 0.155, 0.03, 0.67])
  fig.colorbar(im, cax=cax)
  
  figtype = 'jpg'
  fig.savefig('aaa.jpg',format = figtype,bbox_inches='tight')
  fig.tight_layout()
  </code></pre>
  
  <p>The code succeeds if I comment the following two lines (which is done in the above example):</p>
  
  <pre><code>ax.xlabel(str(i))
  ax.ylabel(str(i))
  </code></pre>
  
  <p>If I use the two lines, I get errors saying:</p>
  
  <pre><code>AttributeError: 'AxesSubplot' object has no attribute 'xlabel'
  </code></pre>
  
  <p>How can I make it correct?</p>
  
  <p>Thank you all for helping me!!!</p>