Sorting out Lipschitz function approximation
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Abstract (arXiv)
Training neural networks under a strict Lipschitz constraint is useful for provable adversarial robustness, generalization bounds, interpretable gradients, and Wasserstein distance estimation. By the composition property of Lipschitz functions, it suffices to ensure that each individual affine transformation or nonlinear activation is 1-Lipschitz. The challenge is to do this while maintaining the expressive power. We identify a necessary property for such an architecture: each of the layers must preserve the gradient norm during backpropagation. Based on this, we propose to combine a gradient norm preserving activation function, GroupSort, with norm-constrained weight matrices. We show that norm-constrained GroupSort architectures are universal Lipschitz function approximators. Empirically, we show that norm-constrained GroupSort networks achieve tighter estimates of Wasserstein distance than their ReLU counterparts and can achieve provable adversarial robustness guarantees with little cost to accuracy.
Key facts. Cited by 213 papers in the map (data through 14 Oct 2026). First posted on arXiv 13 Nov 2018.
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Citing papers per year: 2021: 49; 2022: 30; 2023: 41; 2024: 32; 2025: 33; 2026: 28.
213 papers.
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- 2026Plug-and-Play Methods Provably Converge Even with Improperly Trained Denoisers: Convergence by Architectural Design27 Sep 2026
- 2026Building Trust in Artificial Intelligence: A Necessity for Railway Applications16 Sep 2026
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- 2026Exploring Oversmoothing with Householder Matrices12 Aug 2026
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