Structural Incompatibility of Differentiable Sorting and Within-Vector Rank Normalization

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1. Verfasser: Kim, Taeyun
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Veröffentlicht: 2025
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author Kim, Taeyun
author_facet Kim, Taeyun
contents We show that differentiable sorting and ranking operators are structurally incompatible with within-vector rank normalization. We formalize admissibility through monotone invariance (C1), batch independence (C2), and a rank-space stability condition (C3). Gap-sensitive relaxations such as SoftSort violate (C1) by a quantitative margin that depends on the temperature and input scale. Batchwise rank relaxations such as SinkhornSort violate (C2): the same sample can be assigned outputs arbitrarily close to 0 or 1 depending solely on batch context. Condition (C3) implies (C1) under the rank representation used here and should not be read as a third independent failure mode. We also characterize the admissible class: any admissible operator must factor through the rank representation via a Lipschitz function.
format Preprint
id arxiv_https___arxiv_org_abs_2512_22587
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Structural Incompatibility of Differentiable Sorting and Within-Vector Rank Normalization
Kim, Taeyun
Machine Learning
62G30 (Primary), 68T07 (Secondary)
We show that differentiable sorting and ranking operators are structurally incompatible with within-vector rank normalization. We formalize admissibility through monotone invariance (C1), batch independence (C2), and a rank-space stability condition (C3). Gap-sensitive relaxations such as SoftSort violate (C1) by a quantitative margin that depends on the temperature and input scale. Batchwise rank relaxations such as SinkhornSort violate (C2): the same sample can be assigned outputs arbitrarily close to 0 or 1 depending solely on batch context. Condition (C3) implies (C1) under the rank representation used here and should not be read as a third independent failure mode. We also characterize the admissible class: any admissible operator must factor through the rank representation via a Lipschitz function.
title Structural Incompatibility of Differentiable Sorting and Within-Vector Rank Normalization
topic Machine Learning
62G30 (Primary), 68T07 (Secondary)
url https://arxiv.org/abs/2512.22587