Training-Free Generative Sampling via Moment-Matched Score Smoothing

원문 초록

Diffusion models generate samples by denoising along the score of a perturbed target distribution. In practice, one trains a neural diffusion model, which is computationally expensive. Recent work suggests that score matching implicitly smooths the empirical score, and that this smoothing bias promotes generalization by capturing low-dimensional data geometry. We propose moment-matched score-smoothed overdamped Langevin dynamics (MM-SOLD), a training-free interacting particle sampler that enforces the target moments throughout the sampling trajectory. We prove that the one-particle marginal of the ideal constrained Gibbs equilibrium converges, as the number of particles grows, to a Gibbs--Boltzmann density obtained by exponentially tilting the naive score-smoothed target. Its mean and covariance match the training GMM, even for rank-deficient data. We additionally establish sampling consistency, statistical target-error bounds for bounded data, and consistency of a safeguarded BAOAB-based tilting estimator. Experiments on 2D distributions and latent-space image generation show that MM-SOLD enables fast, robust, latent sampling on CPUs using fixed pretrained autoencoders, with sample fidelity and diversity competitive with neural diffusion baselines.