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Weight decay

As explained in Causal AI

L2 regularization is a regularization method that penalizes the sum of squared parameter values.

Weight decay, treated here as L2 regularization, modifies parameter estimation by adding a penalty proportional to the sum of squared parameter values to the loss. The penalty makes increasingly large parameters increasingly costly, steering optimization away from exceedingly large estimates. section 2.3.4

Operationally, weight decay connects three steps:

  • Begin with a loss function; negative log-likelihood is one example. section 2.3.4
  • Add the squared-parameter term to obtain a regularized objective. section 2.3.4
  • Use numerical optimization to seek parameter values that balance data fit against parameter magnitude. section 2.3.4

Neural-network estimation

When directly finding the likelihood-maximizing parameters is infeasible, optimize a loss augmented with the L2 penalty; the resulting candidate favors smaller parameter values rather than exceedingly large estimates. section 2.3.4

How Causal AI covers it

How deep it goes
Defines the penalty and its effect on large estimates, but does not derive an update rule or implementation procedure.
Examples
Uses neural-network estimation and negative log-likelihood as examples of optimization settings where regularization applies.
What it assumes
Assumes familiarity with model parameters, loss functions, and numerical optimization.
What you can do after
Apply L2 regularization by augmenting a loss with a sum-of-squares parameter penalty.
How it connects
Connects regularization with loss functions, negative log-likelihood, numerical optimization, and neural-network parameter estimation.

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This explainer was generated by Manning's knowledge graph from the text of Causal AI. The section links point to the parts of the book it draws on.