We establish precise structural and risk equivalences between subsampling and ridge regularization for ensemble ridge estimators. Specifically, we prove that linear and quadratic functionals of subsample ridge estimators, when fitted with different ridge regularization levels $\lambda$ and subsample aspect ratios $\psi$, are asymptotically equivalent along specific paths in the $(\lambda, \psi )$-plane (where $\psi$ is the ratio of the feature dimension to the subsample size). Our results only require bounded moment assumptions on feature and response distributions and allow for arbitrary joint distributions. Furthermore, we provide a datadependent method to determine the equivalent paths of $(\lambda, \psi )$. An indirect implication of our equivalences is that optimally-tuned ridge regression exhibits a monotonic prediction risk in the data aspect ratio. This resolves a recent open problem raised by Nakkiran et al. under general data distributions and a mild regularity condition that maintains regression hardness through linearized signal-to-noise ratios.

本文从套索惩罚和子采样的角度建立它们之间结构和风险的等效关系，通过限制不同的岭正则化系数和子采样比例的路径，证明子采样的二阶统计量和岭回归分析的期望风险是等价的，提供一种基于数据推导的确定等价路径的方法，进一步解决了最近由 Nakkiran 等人提出的关于最优化-调整岭回归系数在数据方面比例上是否具有单调预测风险的问题。

子采样和岭正则化之间的广义等价性