Lower Generalization Bounds for GD and SGD in Smooth Stochastic Convex Optimization
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Abstract (arXiv)
This work studies the generalization error of gradient methods. More specifically, we focus on how training steps T and step-size η might affect generalization in smooth stochastic convex optimization (SCO) problems. We first provide tight excess risk lower bounds for Gradient Descent (GD) and Stochastic Gradient Descent (SGD) under the general non-realizable smooth SCO setting, suggesting that existing stability analyses are tight in step-size and iteration dependence, and that overfitting provably happens. Next, we study the case when the loss is realizable, i.e. an optimal solution minimizes all the data points. Recent works show better rates can be attained but the improvement is reduced when training time is long. Our paper examines this observation by providing excess risk lower bounds for GD and SGD in two realizable settings: 1) η T = bigOn, and (2) η T = bigOmegan, where n is the size of dataset. In the first case η T = bigOmegan, our lower bounds tightly match and certify the respective upper bounds. However, for the case η T = bigOmegan, our analysis indicates a gap between the lower and upper bounds. A conjecture is proposed that the gap can be closed by improving upper bounds, supported by analyses in two special scenarios.
Key facts. Cited by 6 papers in the map (data through 7 Oct 2026). Builds on 35 of its 52 references that are in the map. First posted on arXiv 19 Mar 2023.
Builds on
35 of 52 references.
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23 more
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Built on by
Citing papers per year: 2023: 3; 2024: 1; 2025: 1; 2026: 1.
6 papers.
- 2023Fantastic Generalization Measures are Nowhere to be Foundcited by 19
- 2025Fast Last-Iterate Convergence of SGD in the Smooth Interpolation Regimecited by 10
- 2023Select without Fear: Almost All Mini-Batch Schedules Generalize Optimallycited by 5
- 2023Towards Understanding Generalization and Stability Gaps between Centralized and Decentralized Federated Learningcited by 3
- 2024Which Algorithms Have Tight Generalization Bounds?cited by 1
- 2026All ERMs Can Fail in Stochastic Convex Optimization Lower Bounds in Linear Dimensioncited by 0
- 2026All ERMs Can Fail in Stochastic Convex Optimization Lower Bounds in Linear Dimension9 Feb 2026
- 2025Fast Last-Iterate Convergence of SGD in the Smooth Interpolation Regime15 Jul 2025
- 2024Which Algorithms Have Tight Generalization Bounds?2 Oct 2024
- 2023Towards Understanding Generalization and Stability Gaps between Centralized and Decentralized Federated Learning5 Oct 2023
- 2023Fantastic Generalization Measures are Nowhere to be Found24 Sep 2023
- 2023Select without Fear: Almost All Mini-Batch Schedules Generalize Optimally3 May 2023