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Boosting

As explained in Machine Learning Algorithms in Depth

Boosting is an ensemble learning technique that combines weak learners trained sequentially with greater emphasis on previously misclassified examples.

Boosting combines weak learners into a stronger predictive model by training them sequentially. Each round emphasizes examples misclassified earlier, then combines predictions using a weighted vote for classification or weighted sum for regression. section 7.5 section 7.5.2

AdaBoost operationalizes the idea through an adaptive sequence:

  • Initialize all training-example weights equally and fit the first weak classifier. section 7.5.2
  • Increase weights for misclassified examples and decrease weights for correctly classified examples in later rounds. section 7.5.2
  • Measure each learner’s weighted error and assign more influence to more accurate learners. section 7.5.2

Decision stumps provide a concrete base learner: each depth-one tree partitions feature space with a threshold. Gradient tree boosting extends the sequential strategy to differentiable loss functions for classification and regression. section 7.5.2 section 7.5.2

AdaBoost on feature data

A Python implementation trains depth-one decision trees on two Iris features, compares ensembles with 1, 2, 3, and 10 learners, and can also illustrate the method on an XOR dataset. Learning curves and decision regions show how accuracy changes as learners are added.

How Machine Learning Algorithms in Depth covers it

How deep it goes
Explains sequential weighting, weighted errors, and prediction combination, while stating gradient boosting’s loss minimization without fully deriving it.
Examples
Uses depth-one trees, Iris features, an XOR dataset, decision regions, learning curves, and varying ensemble sizes.
What you can do after
Apply it via scikit-learn’s AdaBoostClassifier and evaluate ensembles with different numbers of weak learners.
How it connects
Connects weak learners, decision trees, AdaBoost, gradient boosting, bagging, stacking, weighted voting, and bias–variance tradeoffs.

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This explainer was generated by Manning's knowledge graph from the text of Machine Learning Algorithms in Depth. The section links point to the parts of the book it draws on.