Flow matching, together with classifier-free guidance (CFG), is widely used in generative modeling, yet much of the theoretical understanding remains distribution-wise. Since practical sampling follows individual trajectories, distribution-level guarantees alone do not fully capture how trajectories interact with the data geometry or how guidance reshapes it. To overcome this limitation, we establish a unified stagewise geometric theory of attraction and absorption for both continuous dynamics and explicit Euler discretization. Specifically, with $t\in[0,1]$ running from noise to data, we show that unconditional flow trajectories are successively attracted toward a neighborhood of the global mean, the data convex hull, and a neighborhood of a possibly nonconvex local cluster. Across these stages, the corresponding distance satisfies a common contraction estimate, yielding an $\mathcal{O}(1-t)$ decay of the distance in the final stage. For CFG, the same structure persists with an extrapolated mean, an inflated conditional convex hull, and, near the target cluster, the restored local geometry of conditional flow matching. We further show that a general time schedule $a(t)$ replaces the $\mathcal{O}(1-t)$ decay by $\mathcal{O}(1-a(t))$. Together, these results provide a unified particle-level geometric account of flow matching and CFG across continuous and discrete sampling.
王超,南方科技大学统计与数据科学系副研究员,博导,其研究方向主要为图像处理、科学计算与交叉学科的数据科学。以第一作者或通讯作者身份在Cell子刊、SIAM系列、IEEE汇刊等权威期刊及CCF-A会议发表论文30余篇。入选广东省青年珠江学者,深圳市鹏城孔雀计划特聘岗位,获CVPR研讨会最佳论文奖,CSIAM年会学生论文奖,以及2次获得SIAM差旅奖。主持国家自然科学基金项目两项、省部级基金一项、深圳市科研项目一项。 担任期刊J. Math. Imaging Vision的特刊客座主编。