Module decision_tree 

CART decision trees (ISL ch 8.1) — recursive binary splitting for regression (variance / MSE reduction) and classification (Gini impurity), over a row-major feature matrix. The arena-based node store avoids deep Box recursion. The same builder powers random forests and gradient boosting (with feature subsampling / shallow depth). Scalar split search → CPU.

Structs

DecisionTree

A fitted decision tree.

TreeParams

Tree hyper-parameters.

Enums

Criterion

Split criterion.