A simple generative model based on a continuous-time normalizing flow between any pair of base and target distributions is proposed. The velocity field of this flow is inferred from the probability current of a time-dependent distribution that interpolates between the base and the target in finite time. Unlike conventional normalizing flow inference methods based the maximum likelihood principle, which require costly backpropagation through ODE solvers, our interpolant approach leads to a simple quadratic loss for the velocity itself which is expressed in terms of expectations that are readily amenable to empirical estimation. The flow can be used to generate samples from either the base or target, and can be used to estimate the likelihood at any time along the interpolant. The approach is contextualized in its relation to diffusions. In particular, in situations where the base is a Gaussian distribution, we show that the velocity of our normalizing flow can also be used to construct a diffusion model to sample the target as well as estimating its score. This allows one to map methods based on stochastic differential equations to those of ordinary differential equations, simplifying the mechanics of the model, but capturing equivalent dynamics. Benchmarking on density estimation tasks illustrates that the learned flow can match and surpass maximum likelihood continuous flows at a fraction of the conventional ODE training costs.

本文提出一种基于连续时间正规化流的生成模型，该流的速度场由时间依赖密度的概率流推断而来，可用于样本生成和密度估计，并可最小化插值密度的路径长度来建立最优传输映射。该方法通过对基于随机微分方程的方法的简化，使生成的流可以以低成本超越传统方法，并可在图像生成等任务上达到较理想的性能。

使用随机插值构建归一化流