arXiv Machine Learning By Junyi Lin, Mengyu Li, Jingxuan Hu, Kejun He, Cheng Meng

Beyond Straightness: Non-Crossing Flow Matching via Quantile AlignTree Coupling

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The paper introduces Quantile AlignTree Flow Matching (QAT‑FM), a structured coupling method that builds a hierarchical, quantile‑aligned tree to connect a Gaussian prior with a target distribution. QAT‑FM achieves efficient coupling construction in ≠ Nd log N time and allows per‑pair source sampling in ≠ d time, enabling scalable training for high‑dimensional generative tasks. The authors prove that the coupling preserves marginal consistency, produces non‑crossing interpolation paths, and improves path separation compared to independent coupling, while also extending naturally to conditional generation.

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