title: Return to natural numbers from a logarithmic difference in python
body: <p>I'm working with time series data and have transformed numbers to logarithmic differences with <code>numpy</code>.</p>
  
  <pre><code>df['dlog']= np.log(df['columnx']).diff()
  </code></pre>
  
  <p>Then I made predictions with that transformation.</p>
  
  <p>How can I return to normal numbers?</p>