arXiv Machine Learning By Prathamesh Dharangutte, Amartya Sanyal

New Lower Bounds for Private PAC Learning

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The paper investigates realizable PAC learning under approximate differential privacy and develops a framework for establishing lower bounds on sample complexity. It demonstrates that classes sharing the same VC and Littlestone dimensions can have different private sample complexities, introducing the Independent Class Packing (ICP) parameter to capture this distinction. Using ICP, the authors derive tight lower bounds for several hypothesis classes, including axis-aligned rectangles, unions of intervals, linear subspaces, and improved bounds for halfspaces and convex polygons, and show that ICP characterizes private PAC sample complexity for product classes up to logarithmic factors.

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arXiv Machine Learning
Sep 25

Bandit Multiclass PAC Learning: Corrected Lower Bounds, Exact Families, and a Confidence Direct-Sum Phenomenon

The paper revisits realizable multiclass PAC learning with bandit feedback, correcting a previously claimed lower bound on sample complexity. It introduces a new anchored dimension, “aBDS,” and establishes a constant‑free three‑part lower bound, while also providing tighter upper bounds that eliminate dependence on the total label count. The authors demonstrate that the optimal sample complexity can vary dramatically even among classes with identical dimensional profiles, revealing a confidence direct‑sum phenomenon and a rank‑saturation phase transition.

By Guangjian Zhang