Apple 研究：扩散模型置信度排序的局限性
Limits of Confidence in Diffusion
Apple 研究团队从理论上证明，扩散模型（含 remasking 与 uniform-state 采样器）的每一步只有在所写入位置在已固定 token 条件下相互独立时，才与训练分布匹配，而任何逐位置分布的乘积都无法匹配存在依赖关系的 token 组。
AuthorsRuss Webb, Amitis Shidani, Alice Bizeul, Dan Busbridge
Discrete diffusion, including remasking and uniform-state samplers, generate a sequence by writing multiple token positions per step, drawing each from a per-position distribution and choosing which positions to write from those same distributions. For domains of general interest (pixels, phonemes, or words) there are inherent dependencies between tokens. We show that a step matches the training distribution only when the positions it writes are conditionally independent given the tokens already fixed, that no product of per-position distributions can match a dependent group, and that per-position distributions do not determine whether a group is dependent: two joint distributions can have identical per-position marginals while differing in which combinations of values occur. On ScanAndAdd, a synthetic task whose joint distribution is available in closed form, we verify that every group of two or more undetermined positions a confidence ranking writes is dependent, and measure the generated distribution to be 29× the sampling-noise floor total variation while per-sample metrics are 1.0.
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来源：Apple Machine Learning Research · machinelearning.apple.com