title: Matplotlib.Pyplot does not show output; No Error
body: <p>My platform is as follows</p>
  
  <p>Centos 6.x (VirtualBox VM running on Win-7 host),
  Python 2.6.6,
  Matplotlib 1.3.1,
  Numpy 1.8.0,
  Scipy 0.14.0.dev-bb608ba</p>
  
  <p>I am running the below histogram.py code</p>
  
  <pre><code>#!/usr/bin/env python
  
  import numpy as np
  import matplotlib.pyplot as plt
  
  mu, sigma = 0, 1 # mean and standard deviation
  f = np.random.normal(mu, sigma, 1000) # generate feature-vector with normal distribution
  
  # plot the histogram - check the distribution
  count, bins, ignored = plt.hist(f, 30, normed=True)
  
  plt.plot(bins, 1/(sigma * np.sqrt(2 * np.pi)) *
                  np.exp( - (bins - mu)**2 / (2 * sigma**2) ),
          linewidth=2, color='r')
  plt.xlabel('Values')
  plt.ylabel('Probability')
  plt.title('Histogram')
  plt.text(60, .025, r'$\mu=0,\ \sigma=1$')
  plt.axis([-0.4, 0.3, 0, 5])
  plt.grid(True)
  plt.show()
  </code></pre>
  
  <p>But no output plot is appearing. I am receiving no error, so getting difficult to debug.</p>
  
  <p>Following are the rc file-location and backend for my matplotlib installation</p>
  
  <pre><code>[hue@sandbox ~]$ python
  Python 2.6.6 (r266:84292, Jul 10 2013, 22:48:45)
  [GCC 4.4.7 20120313 (Red Hat 4.4.7-3)] on linux2
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt; import matplotlib
  &gt;&gt;&gt; matplotlib.matplotlib_fname()
  '/usr/lib64/python2.6/site-packages/matplotlib-1.3.1-py2.6-linux-x86_64.egg/matplotlib/mpl-data/matplotlibrc'
  &gt;&gt;&gt; matplotlib.get_backend()
  'agg'
  </code></pre>
  
  <p>Do I need to modify my 'agg' backend to 'Qt4Agg' or something else? Does it need me to modify the rc file?</p>
  
  <p>Note: I checked my matplotlibrc file to have only <code>backend    : agg</code>. Rest all parameters are commented. </p>
  
  <p>As per below comments, I tried installing libpng but facing the below error:</p>
  
  <pre><code>pngfix.o: In function `zlib_reset':
  /usr/lib/hue/libpng-1.6.6/contrib/tools/pngfix.c:2151: undefined reference to `inflateReset2'
  collect2: ld returned 1 exit status
  </code></pre>
  
  <p>I have now successfully installed a stable and working duo of libpng-1.5.9/zlib-1.2.7 instead of the previous unstable versions libpng-1.6.6/zlib-1.2.8 and both the libs are successfully installed.</p>
  
  <p>But despite having a working and stable libpng, I can't open the png file being generated by the python code (given above). Is there any specific configuration setting for VMs to open .png files? How exactly can .png files be opened on Linux VMs running on WIndows host?</p>