title: What is the difference between num_boost_round and n_estimators
body: <p>I saw that some <code>xgboost</code> methods take a parameter <code>num_boost_round</code>, like this:</p>
  
  <pre><code>model = xgb.cv(params, dtrain,  num_boost_round=500, early_stopping_rounds=100)
  </code></pre>
  
  <p>Others however take <code>n_estimators</code> like this:</p>
  
  <pre><code>model_xgb = xgb.XGBRegressor(n_estimators=360, max_depth=2, learning_rate=0.1)
  </code></pre>
  
  <p>As far as I understand, each time boosting is applied a new estimator is created. Is that nor correct?</p>
  
  <p>If that is so, then the numbers <code>num_boost_round</code> and  <code>n_estimators</code> should be equal, right?</p>