| Interface | Description | 
|---|---|
| Impurity | Trait for calculating information gain. | 
| Class | Description | 
|---|---|
| Entropy | Class for calculating entropy during multiclass classification. | 
| Gini | Class for calculating the Gini impurity
 (http://en.wikipedia.org/wiki/Decision_tree_learning#Gini_impurity)
 during multiclass classification. | 
| Impurities | Factory for Impurity instances. | 
| Variance | Class for calculating variance during regression |