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Surrogate model

As explained in Machine Learning for Tabular Data: XGBoost, Deep Learning, and AI

A surrogate function is an approximate model of an objective function that predicts objective behavior across untested parameter settings.

A surrogate model is an approximate model of an objective function. In Bayesian optimization, it predicts model performance across untested hyperparameter settings, reducing the need to evaluate every combination directly. section 6.3.4

A practical Bayesian optimization loop works as follows:

  • Build or update the surrogate from feedback produced by the objective function. section 6.3.4
  • Use an acquisition function to balance exploration of uncertain settings with exploitation of promising settings. section 6.3.4
  • Choose the next hyperparameters, evaluate the model, and repeat the fine-tuning cycle. section 6.3.4

Tuning an XGBoost classifier

An Optuna study can search settings such as learning rate, tree depth, subsampling, and regularization, then report the best parameters and validation score after 60 trials.

How Machine Learning for Tabular Data: XGBoost, Deep Learning, and AI covers it

How deep it goes
Explains updates, acquisition, exploration, exploitation, and model choices, but does not derive their mathematics.
Examples
Demonstrates Optuna tuning an XGBoost classifier and inspecting optimization history and hyperparameter importance.
What it assumes
Assumes familiarity with model hyperparameters and objective performance while introducing surrogate-guided search conceptually.
What you can do after
Apply it via Optuna to search XGBoost hyperparameters and inspect the resulting best configuration and score.
How it connects
Connects Bayesian optimization with acquisition functions, objective functions, Gaussian processes, random forests, and tree-structured Parzen estimators.

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This explainer was generated by Manning's knowledge graph from the text of Machine Learning for Tabular Data: XGBoost, Deep Learning, and AI. The section links point to the parts of the book it draws on.