title: What is the difference between Freidman mse and mse?
body: <p>I'm looking into a <code>GradientBoostingClassifier</code> in <code>sklearn</code>. Then, I found there are 3 kind of criterion. Friedman mse, mse, mae.
  the descriptions provided by <code>sklearn</code> are:</p>
  
  <blockquote>
    <p>The function to measure the quality of a split. Supported criteria are “friedman_mse” for the mean squared error with improvement score by Friedman, “mse” for mean squared error, and “mae” for the mean absolute error. The default value of “friedman_mse” is generally the best as it can provide a better approximation in some cases.</p>
  </blockquote>
  
  <p>I can't understand what is different?
  Who's gonna let me know?</p>
  
  <p>thanks!</p>