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Understanding diffusion models requires rethinking (again) generalization
Published:
We argue that the field should pivot from explaining why the diffusion models do not memorize to investigating what the model actually learns during pre-memorization phase.
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publications
Comptes Rendus Mathématique · 2022
More on lines in Euclidean Ramsey theory
A two-colouring of Euclidean space in every dimension with no red l_3 and no blue l_m.
- Question. Can Euclidean space be two-coloured, in every dimension, with no red copy of three equally spaced points on a line and no blue copy of some longer such configuration?
- Result. Yes: for some natural number m there is a red/blue colouring of Euclidean space in every dimension with no red copy of l_3 and no blue copy of l_m, answering a question of Conlon and Fox, and independently of Arman and Tsaturian.
David Conlon and Yu-Han Wu (2023). More on lines in Euclidean Ramsey theory. Comptes Rendus. Mathématique, 361(G5), 897–901.
@article{conlon2023more,
title={More on lines in {Euclidean} {Ramsey} theory},
author={Conlon, David and Wu, Yu-Han},
journal={Comptes Rendus. Math{\'e}matique},
volume={361},
number={G5},
pages={897--901},
year={2023}
}ICLR 2024 Spotlight
Implicit regularization of deep residual networks towards neural ODEs
Residual networks initialized as neural ODE discretizations stay so throughout gradient-flow training.
- Problem. The link between residual networks and their continuous-depth analogue, neural ODEs, lacked a mathematical foundation.
- Approach. Study gradient flow on deep residual networks initialized as discretizations of a neural ODE.
- Result. The discretization structure is preserved throughout training, for finite time and, under a Polyak–Łojasiewicz condition, as time goes to infinity, with convergence to a global minimum.
Pierre Marion, Yu-Han Wu, Michael E. Sander and Gérard Biau (2024). Implicit regularization of deep residual networks towards neural ODEs. In The Twelfth International Conference on Learning Representations (ICLR).
@inproceedings{marion2024implicit,
title={Implicit regularization of deep residual networks towards neural {ODEs}},
author={Marion, Pierre and Wu, Yu-Han and Sander, Michael E. and Biau, G{\'e}rard},
booktitle={The Twelfth International Conference on Learning Representations ({ICLR})},
year={2024}
}COLT 2025
Taking a Big Step: Large Learning Rates in Denoising Score Matching Prevent Memorization
Large learning rates implicitly regularize denoising score matching and prevent memorization.
- Problem. The exact minimizer of denoising score matching memorizes the training data, yet trained models memorize only mildly.
- Approach. Analyze gradient descent with large steps, which can only converge to minima whose sharpness is bounded by the inverse learning rate.
- Result. The memorizing solution is too sharp to be reached; large learning rates prevent memorization.
Yu-Han Wu, Pierre Marion, Gérard Biau and Claire Boyer (2025). Taking a Big Step: Large Learning Rates in Denoising Score Matching Prevent Memorization. In Proceedings of the Thirty Eighth Conference on Learning Theory (COLT), PMLR 291:5718–5756.
@inproceedings{wu2025taking,
title={Taking a Big Step: Large Learning Rates in Denoising Score Matching Prevent Memorization},
author={Wu, Yu-Han and Marion, Pierre and Biau, G{\'e}rard and Boyer, Claire},
booktitle={Proceedings of the Thirty Eighth Conference on Learning Theory ({COLT})},
series={Proceedings of Machine Learning Research},
volume={291},
pages={5718--5756},
year={2025}
}ICML 2026 Oral at the PriGM workshop, EurIPS 2025
Optimal Stopping in Latent Diffusion Model
Why the last denoising steps of a latent diffusion model can hurt, and when to stop.
- Problem. The last steps of latent diffusion can degrade samples, which does not happen in pixel-space diffusion.
- Approach. A Gaussian model with linear autoencoders that links latent dimension, the constraints of score matching and the stopping time.
- Result. Low-dimensional latents call for earlier stopping, high-dimensional ones for later; stopping time is a key hyperparameter of latent diffusion.
Yu-Han Wu, Quentin Berthet, Gérard Biau, Claire Boyer, Romuald Elie and Pierre Marion (2026). Optimal Stopping in Latent Diffusion Models. In International Conference on Machine Learning (ICML).
@inproceedings{wu2026optimal,
title={Optimal Stopping in Latent Diffusion Models},
author={Wu, Yu-Han and Berthet, Quentin and Biau, G{\'e}rard and Boyer, Claire and Elie, Romuald and Marion, Pierre},
booktitle={International Conference on Machine Learning ({ICML})},
year={2026}
}NeurIPS 2026
MIND: Monge Inception Distance for Generative Models Evaluation
A sliced-Wasserstein alternative to FID: more sample-efficient, faster, and more robust.
- Problem. FID needs tens of thousands of samples and can be fooled by matching moments.
- Approach. A sliced Wasserstein distance between Inception features, computed by sorting one-dimensional projections, with no high-dimensional means or covariances to estimate.
- Result. An order of magnitude more sample-efficient, two orders of magnitude faster, more robust; 5k samples match FID at 50k.
Quentin Berthet, Yu-Han Wu, Clément Crepy, Romuald Elie, Klaus Greff and Michael E. Sander (2026). MIND: Monge Inception Distance for Generative Models Evaluation. arXiv:2605.06797.
@misc{berthet2026mind,
title={{MIND}: Monge Inception Distance for Generative Models Evaluation},
author={Berthet, Quentin and Wu, Yu-Han and Crepy, Cl{\'e}ment and Elie, Romuald and Greff, Klaus and Sander, Michael E.},
year={2026},
eprint={2605.06797},
archivePrefix={arXiv},
primaryClass={cs.LG}
}NeurIPS 2026 position track
Understanding diffusion models requires rethinking (again) generalization
Generalization in diffusion models needs new theory: what is learned before memorization?
- Problem. In diffusion models memorization and generalization are incompatible, so the supervised-learning theory of generalization does not transfer.
- Approach. Survey the three families of explanations and run controlled CIFAR-10 sweeps over dataset size, model size, batch size and learning rate.
- Position. Why models do not memorize is largely settled by early stopping and the linear scaling of memorization time; what is learned before memorization is the open question.
Pierre Marion and Yu-Han Wu (2026). Understanding diffusion models requires rethinking (again) generalization. arXiv:2605.06077.
@misc{marion2026understanding,
title={Understanding diffusion models requires rethinking (again) generalization},
author={Marion, Pierre and Wu, Yu-Han},
year={2026},
eprint={2605.06077},
archivePrefix={arXiv},
primaryClass={cs.LG}
}arXiv preprint · 2026
DiffusionGemma
An open-weight discrete-diffusion language model fine-tuned from Gemma 4.
- Problem. Autoregressive LLMs decode one token at a time, a sequential bottleneck for generation speed.
- Approach. Fine-tune Gemma 4 into a block-diffusion model that refines 256 tokens in parallel: supervised denoising, then reinforcement learning with sampler distillation, using under 10% of the base model’s training tokens.
- Result. About 1,500 output tokens per second on a single H100, a new speed-capability Pareto frontier, while keeping thinking mode, multimodal inputs and long context.
DiffusionGemma Team (2026). DiffusionGemma Technical Report. arXiv:2608.00146.
@misc{diffusiongemma2026,
title={{DiffusionGemma} Technical Report},
author={{DiffusionGemma Team}},
year={2026},
eprint={2608.00146},
archivePrefix={arXiv},
primaryClass={cs.LG}
}arXiv preprint · 2026
Kastor: An efficient fine-tuning strategy for generative emulation of PDE simulation
Fine-tunes a deterministic physics foundation model into a fast, accurate generative PDE emulator.
- Problem. Autoregressive ML emulators of PDEs accumulate error over long horizons and miss the stochasticity of physical systems.
- Approach. Adapt a deterministic physics foundation model into a generative surrogate with two-stage inference, mean-prediction regularization and spatial gradient matching.
- Result. 42.9% average reduction in forecasting error over the Walrus fine-tuning baseline on The Well, better on 8 of 10 datasets.
Guillaume Couairon, Alexis Jacq, Yu-Han Wu, Renu Singh, Yana Hasson, Quentin Berthet and Romuald Elie (2026). Kastor: An efficient fine-tuning strategy for generative emulation of PDE simulations. arXiv:2608.06107.
@misc{couairon2026kastor,
title={Kastor: An efficient fine-tuning strategy for generative emulation of {PDE} simulations},
author={Couairon, Guillaume and Jacq, Alexis and Wu, Yu-Han and Singh, Renu and Hasson, Yana and Berthet, Quentin and Elie, Romuald},
year={2026},
eprint={2608.06107},
archivePrefix={arXiv},
primaryClass={cs.LG}
}talks
Journées de Statistique 2025
Published:
Oral presentation of Taking a Big Step: Large Learning Rates in Denoising Score Matching Prevent Memorization.
COLT 2025
Published:
Oral presentation of Taking a Big Step: Large Learning Rates in Denoising Score Matching Prevent Memorization.
PriGM Workshop, EurIPS 2025
Published:
Oral presentation of Optimal Stopping in Latent Diffusion Models, selected for an oral session at the PriGM workshop of EurIPS 2025.
Lemanth 2026
Published:
Poster presentation of MIND: Monge Inception Distance for Generative Models Evaluation.
Optimisation et Apprentissage appliqués aux contenus numériques
Published:
Invited talk at USPN on Understanding diffusion models requires rethinking (again) generalization.