Hyperparameter tuning searches for settings that improve a model’s evaluation objective. A reliable process defines the search space, uses cross-validation, and selects a search algorithm that balances quality, computation, and time. section 6.3
A practical tuning workflow includes:
- Define the evaluation metric and the hyperparameters whose effects matter. section 6.3
- Build cross-validation so promising settings generalize beyond the available data rather than overfitting it. section 6.3
- Choose a search strategy that finds suitable settings within practical computational cost. section 6.3
Tuning an XGBoost regressor
For the Tokyo Airbnb regression problem, Optuna evaluates 60 trials using cross-validated mean absolute error. It explores boosters, objectives, estimators, learning rate, sampling ratios, and tree depth. One resulting configuration uses a gbtree booster, 901 estimators, depth seven, and a Tweedie objective, reducing MAE from the initial attempt. section 7.2.5

















