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Use MSE criterion in base tree regressor #492

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Use MSE criterion in base tree regressor #492

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39f64c1
Use MSE criterion in base tree regressor
slievens Oct 14, 2026
ce1ee48
No leaf has a split_score.
slievens Oct 15, 2026
6505833
Remove gini and tests
slievens Oct 15, 2026
d4e67bc
Clamp mass residue to zero
slievens Oct 15, 2026
be58518
Merge 'always-shuffle'
slievens Oct 17, 2026
e7a8008
Use a stable MSE improvement and drop zero-mass rows
slievens Oct 18, 2026
501e5d5
Refactor grow
slievens Oct 18, 2026
c7eb8a3
update changelog
slievens Oct 18, 2026
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2 changes: 2 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
## [Unreleased]

- In the `...Regressor`s the features are always shuffled even when `mtry` equals the number of attributes. This changes the constructed trees.
- `tree`: `BaseTreeRegressor` (used by `DecisionTreeRegressor`, `RandomForestRegressor` and `ExtraTreesRegressor`) uses a new internal `Criterion` trait with `MSECriterion`. The MSE split improvement uses a numerically stable formula. The selected splits do not change when a constant is added to y. Exactly tied splits can be broken in a different way, so fitted trees can differ slightly from earlier versions.
- `tree`: in the `...Regressor`s, rows with sample weight 0 are removed before the tree grows. They no longer count toward `min_samples_leaf` and `min_samples_split`, and they no longer move a split threshold. A tree fitted with a zero-weight row is the same as a tree fitted without that row.

## [0.6.16]
### Fixed
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