From Order to Distribution: An Exact Operator Framework for Forgetting in Continual Learning
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Abstract (arXiv)
A central challenge in continual learning is forgetting: the loss of performance on previously learned tasks after learning new ones. Prior theory has analyzed forgetting under random orderings of fixed task collections in overparameterized linear regression. We shift the focus from task order to task distribution, asking how its structure determines forgetting. In the linear setting with a shared solution, i.i.d. task sampling, and sequential exact fitting, we derive an exact operator identity expressing historical forgetting directly in terms of the task distribution. Building on this identity, we establish an exponential decay guarantee for expected historical forgetting under every fixed task distribution in finite dimensions, characterize its asymptotic behavior, and relate decay to the distribution's coverage of observable directions. For an individual learned task, we show that subsequent tasks can collectively support recovery without exact revisits. We derive a lower bound on recovery time and construct a task distribution attaining its inverse-coverage scaling.
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References · 35
- 2016Overcoming catastrophic forgetting in neural networkscited by 4,787
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- 2022How catastrophic can catastrophic forgetting be in linear regression?cited by 81
23 more
- 2023Theory on Forgetting and Generalization of Continual Learningcited by 72
- 2022Continual evaluation for lifelong learning: Identifying the stability gapcited by 56
- 2023Continual Learning in Linear Classification on Separable Datacited by 34
- 2024A Statistical Theory of Regularization-Based Continual Learningcited by 33
- 2024Understanding Forgetting in Continual Learning with Linear Regressioncited by 30
- 2022Analysis of Catastrophic Forgetting for Random Orthogonal Transformation Tasks in the Overparameterized Regimecited by 29
- 2024The Joint Effect of Task Similarity and Overparameterization on Catastrophic Forgetting -- An Analytical Modelcited by 26
- 2021Statistical Mechanical Analysis of Catastrophic Forgetting in Continual Learning with Teacher and Student Networkscited by 22
- 2024Disentangling and Mitigating the Impact of Task Similarity for Continual Learningcited by 19
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- 2024Theoretical Insights into Overparameterized Models in Multi-Task and Replay-Based Continual Learningcited by 11
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- 2025Convergence and Implicit Bias of Gradient Descent on Continual Linear Classificationcited by 9
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- 2025Replay Can Provably Increase Forgettingcited by 5
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- 2017Preasymptotic Convergence of Randomized Kaczmarz Methodcited by 1
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