Diffusion models, which convert noise into new data instances by learning to reverse a diffusion process, have become a cornerstone in contemporary generative modeling. In this work, we develop non-asymptotic convergence theory for a popular diffusion-based sampler (i.e., the probability flow ODE sampler) in discrete time, assuming access to $\ell_2$-accurate estimates of the (Stein) score functions. For distributions in $\mathbb{R}^d$, we prove that $d/\varepsilon$ iterations -- modulo some logarithmic and lower-order terms -- are sufficient to approximate the target distribution to within $\varepsilon$ total-variation distance. This is the first result establishing nearly linear dimension-dependency (in $d$) for the probability flow ODE sampler. Imposing only minimal assumptions on the target data distribution (e.g., no smoothness assumption is imposed), our results also characterize how $\ell_2$ score estimation errors affect the quality of the data generation processes. In contrast to prior works, our theory is developed based on an elementary yet versatile non-asymptotic approach without the need of resorting to SDE and ODE toolboxes.

本研究解决了扩散模型在生成建模中的收敛问题，提出了一种基于基本非渐近方法的概率流常微分方程采样器的收敛理论。研究表明，在满足最小假设条件下，使用$ \ell_2 $精确估计的Stein得分函数，经过$d/\varepsilon$次迭代即可将目标分布近似至$\varepsilon$的全变差距离，显著提高了对数据生成过程的理解。

扩散模型概率流常微分方程的快速收敛理论