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Quadratic approximation

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

A second-order approximation estimates a function locally using both its first and second derivatives.

A quadratic approximation improves local optimization by using both first- and second-derivative information. In XGBoost, this second-order approximation is one of the techniques used for quicker gradient-boosting optimization. section 5.4.2

Newtonian boosting update

A Newtonian gradient-boosting implementation calculates a gradient and Hessian, then trains a decision tree on the adjusted target -gradient / (hessian + reg_lambda). With a constant Hessian and regularization value 0.25, the second-order information directly influences each prediction update.

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

How deep it goes
Defines second-order optimization and demonstrates gradient, Hessian, and regularized tree-target calculations without deriving the approximation.
Examples
Demonstrates a NewtonianGradientBoosting class whose tree targets divide gradients by regularized Hessians.
What you can do after
Evaluate how XGBoost uses second-order information to update predictions and accelerate gradient-boosting optimization.
How it connects
Connects quadratic approximation with gradient boosting, Newton-Raphson methods, Hessians, decision trees, and regularization.

Related concepts

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.