arXiv:2605.13681cs.LGstat.ML2026-05

提出一种更符合流语言模型特性的采样方法,提升生成质量与多样性。

Sampling from Flow Language Models via Marginal-Conditioned Bridges

论文配图:Sampling from Flow Language Models via Marginal-Conditioned Bridges
图 1 · 摘自论文原文
  • 基于后验预测采样,每步从各位置边际分布中采出真实单热序列作为终点
  • 在相同计算量下,生成文本质量更高、多样性更好,且误差可量化
  • 无需训练,支持温度调节等细粒度控制,适合需要精确生成的场景

流语言模型(FLMs)将连续流匹配应用于独热编码的词元序列,其去噪器具有特殊结构:每个去噪均值块是该位置干净词元的后验边际分布。标准DDPM式采样会将这些边际坍缩为单一条件均值终点,该终点通常不是有效独热序列。我们主张,对FLM而言自然的采样方式应为后验预测采样:每一步反向过程中,从由FLM词元边际定义的因子化后验中采样一个干净的独热终点,并基于该终点采样下一个连续状态,使用解析的Ornstein--Uhlenbeck桥。该方法无需训练,仅需与标准采样相同的模型评估次数,且为词元级解码控制(如温度调节、核截断)提供合理接口。我们证明,在后验边际精确时,终点近似误差恰好等于词元位置间的条件多信息量。诱导的一步桥核保留了所有词元级后验预测边际,仅损失残余的跨位置依赖。最后,通过Girsanov路径空间比较证明,边际条件桥的去噪误差项不大于冻结条件均值桥,只要中间坐标桥观测揭示额外关于干净词元的信息,即存在严格改进。实验表明,该采样器在FLMs上显著改善了质量-多样性权衡。代码已开源:github.com/imbirik/mcb。

原文摘要 · Abstract (English)

Flow Language Models (FLMs) are a recently introduced class of language models which adapt continuous flow matching for one-hot encoded token sequences. Their denoisers have a special structure absent from generic continuous diffusion models: each block of the denoising mean is a posterior marginal distribution over the clean token at that position. Standard DDPM-style samplers collapse these marginals to a single conditional-mean endpoint and bridge toward this simplex-valued point, which is generally not a valid one-hot sequence. We argue that the natural sampler for an FLM is instead posterior-predictive. At each reverse step, we sample a clean one-hot endpoint from the factorized posterior defined by the FLM token marginals, and then sample the next continuous state from the analytic Ornstein--Uhlenbeck bridge conditioned on that endpoint. The method is training-free, uses the same model evaluations as standard sampling, and gives a principled interface for token-level decoding controls such as temperature scaling and nucleus truncation. We show that, under exact posterior marginals, the endpoint approximation error is exactly the conditional multi-information among token positions. The induced one-step bridge kernel preserves all token-wise posterior-predictive marginals and loses only the residual cross-position dependence. Finally, we prove a Girsanov path-space comparison showing that the marginal-conditioned bridge has a no-larger denoising-error term than the frozen conditional-mean bridge, with strict improvement whenever intermediate coordinate-wise bridge observations reveal additional information about the clean token. Experiments with FLMs show that the sampler improves the quality--diversity tradeoff. Code is available at: github.com/imbirik/mcb.

流模型语言生成采样优化后验预测

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