title: bug of autocorrelation plot in matplotlib‘s plt.acorr?
body: <p>I am plotting autocorrelation with python. I used three ways to do it: 1. pandas, 2. matplotlib, 3. statsmodels. I found the graph I got from matplotlib is not consistent with the other two. The code is:</p>
  
  <pre><code> from statsmodels.graphics.tsaplots import *
   # print out data
   print mydata.values
  
   #1. pandas
   p=autocorrelation_plot(mydata)
   plt.title('mydata')
  
   #2. matplotlib
   fig=plt.figure()
   plt.acorr(mydata,maxlags=150)
   plt.title('mydata')
  
   #3. statsmodels.graphics.tsaplots.plot_acf
   plot_acf(mydata)
   plt.title('mydata')
  </code></pre>
  
  <p>The graph is here: <a href="http://quant365.com/viewtopic.php?f=4&amp;t=33" rel="noreferrer">http://quant365.com/viewtopic.php?f=4&amp;t=33</a></p>