Penalty
Regularisation knob shared across regression stats. The mathematical effect is always the same; the mechanics differ per host: a closed-form read()-time projection in UnivariateRegressionStat, lazy multiplicative scaling / truncated-gradient in StochasticRegressionStat, per-coordinate proximal step (L1) or gradient term (L2) in DiagonalRegressionStat. See each stat's KDoc.