Population dynamics is the study of temporal and spatial variation in the size of populations of organisms and is a major part of population ecology. One of the main difficulties in analyzing population dynamics is that we can only obtain observation data with coarse time intervals from fixed-point observations due to experimental costs or other constraints. Recently, modeling population dynamics by using continuous normalizing flows (CNFs) and dynamic optimal transport has been proposed to infer the expected trajectory of samples from a fixed-point observed population. While the sample behavior in CNF is deterministic, the actual sample in biological systems moves in an essentially random yet directional manner. Moreover, when a sample moves from point A to point B in dynamical systems, its trajectory is such that the corresponding action has the smallest possible value, known as the principle of least action. To satisfy these requirements of the sample trajectories, we formulate the Lagrangian Schr\"odinger bridge (LSB) problem and propose to solve it approximately using neural SDE with regularization. We also develop a model architecture that enables faster computation. Our experiments show that our solution to the LSB problem can approximate the dynamics at the population level and that using the prior knowledge introduced by the Lagrangian enables us to estimate the trajectories of individual samples with stochastic behavior.

本研究提出了使用连续标准化流（CNFs）和动态最优输运方法对种群动态进行建模，以在固定时间点观测到的种群中推断采样轨迹的方法。通过使用正则化神经SDE对对流扩散过程进行建模并开发了一个模型架构，可以有效地近似种群级别的动态，即使在高维数据中也可以实现，并且使用拉格朗日方法引入的先验知识可以估计具有随机行为的采样级别动态。

神经拉格朗日薛定谔桥：扩散模型用于人口动态