title: Matplotlib graph expand the x axis
body: <p>I  have the following <a href="https://i.stack.imgur.com/cFAL2.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cFAL2.png" alt="graph"></a>.</p>
  
  <pre><code>import matplotlib.pyplot as plt 
  import numpy as np
  fig = plt.figure()
  
  
  x_values = [2**6,2**7,2**8,2**9,2**10,2**12]
  y_values_ST = [7.3,15,29,58,117,468]     
  y_values_S3 = [2.3,4.6,9.1,19,39,156]     
  xticks=['2^6','2^7','2^8','2^9','2^10','2^12']
  
  plt.plot(x_values, y_values_ST,'-gv')
  plt.plot(x_values, y_values_S3,'-r+')
  plt.legend(['ST','S^3'], loc='upper left')
  plt.xticks(x_values,xticks)
  
  fig.suptitle('Encrypted Query Size Overhead')
  plt.xlabel('Query size')
  plt.ylabel('Size in KB')
  plt.grid()
  fig.savefig('token_size_plot.pdf')
  plt.show()
  </code></pre>
  
  <p>1)How i can delete the last gap as shown after 2^12?
  2)How i can spread more the values in the x axis such that the first two values are not overlapped?</p>