title: Extrapolate Pandas DataFrame
body: <p>It is easy to interpolate values in a <code>Pandas.DataFrame</code> using <code>Series.interpolate</code>, how can extrapolation be done?</p>
  
  <p>For example, given a DataFrame as shown, how can we extrapolate it 14 more months to 2014-12-31? Linear extrapolation is fine.</p>
  
  <pre><code>X1 = range(10)
  X2 = map(lambda x: x**2, X1)
  df = pd.DataFrame({'x1': X1, 'x2': X2},  index=pd.date_range('20130101',periods=10,freq='M'))
  </code></pre>
  
  <p>I am thinking that a new DataFrame must first be created, with the DateTimeIndex starting from 2013-11-31 and extending for 14 more <code>M</code> periods. Beyond that I'm stuck.</p>
  
  <p><a href="https://i.stack.imgur.com/CAV1k.png" rel="noreferrer"><img src="https://i.stack.imgur.com/CAV1k.png" alt="enter image description here"></a></p>