title: How can I get matplotlib work correctly
body: <p>Recently I am learning to using nltk on Windows 7. I installed Python2.7 and NumPy1.6.2 and matplotlib 1.3.0 for Python 2.7. But when I try to run the following code it just won't work(The first line works correctly):</p>
  
  <pre><code>from nltk.book import *
  text4.dispersion_plot(["citizens", "democracy", "freedom", "duties", "America"])
  </code></pre>
  
  <p>The code is from the book of <em>Natural Languages Processing with Python</em>. The error information is as followed:</p>
  
  <pre><code>Traceback (most recent call last):
    File "&lt;pyshell#6&gt;", line 1, in &lt;module&gt;
      text4.dispersion_plot(["citizens", "democracy", "freedom", "duties", "America"])
    File "D:\Program Files\Python27\lib\site-packages\nltk\text.py", line 456, in dispersion_plot
      dispersion_plot(self, words)
    File "D:\Program Files\Python27\lib\site-packages\nltk\draw\dispersion.py", line 27, in dispersion_plot
      raise ValueError('The plot function requires the matplotlib package (aka pylab).'
  ValueError: The plot function requires the matplotlib package (aka pylab).See http://matplotlib.sourceforge.net/
  </code></pre>
  
  <p>How can I get it work correctly? Thanks a lot.</p>