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DDPM Score Matching and Distribution Learning (Extended Abstract)
Proceedings of Thirty Ninth Conference on Learning Theory, PMLR 336:1434-1435, 2026.
Abstract
Score estimation is the backbone of score-based generative models (SGMs), and particularly denoising diffusion probabilistic models (DDPMs). A fundamental theoretical result in this area is that, given access to accurate score estimates, SGMs can efficiently generate from any realistic data distribution (Chen, Chewi, Li, Li, Salim, and Zhang, ICLR’23; Lee, Lu, and Tan, ALT’23). This can be viewed as a result on distribution learning, where the learned distribution is implicit as the law of the output of a sampler. However, it is unclear how score estimation relates to more classical forms of distribution learning, such as parameter estimation and density estimation. We present a framework reducing the other two forms of distribution learning to score estimation, which has various implications in statistical and computational learning theory: parameter estimation, where denoising score matching in DDPMs is asymptotically efficient; density estimation, where estimated scores can be lifted to a $(\epsilon,\delta)$-PAC density estimator and yield minimax rates over Hölder classes and a quasi-polynomial PAC density estimation algorithm for Gaussian location mixtures; and lower bounds for score estimation, where PAC density estimation yields computational lower bounds for score estimation of general distribution families and cryptographic lower bounds for score estimation of general Gaussian mixture models.