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A quantitative tree-likeness bound from average hyperbolicity
Abstract
Chatterjee and Sloman proved that a bounded measurable similarity function with sufficiently small average Gromov hyperbolicity admits a tree representation with small mean approximation error. Their argument uses a weighted version of Szemerédi's regularity lemma and does not yield explicit quantitative bounds. Here, we establish a tighter relation between average hyperbolicity and mean tree approximation error. For a similarity function s:S× S→[0,b], we prove that Tree(s) ≤ (63/e)1/3 √[3]b2 Hyp(s) ≤ 2.8512 √[3]b2 Hyp(s). The proof uses a simple pivoting construction inspired by \KwikCluster. We also discuss the optimal dependence on average hyperbolicity, including a square-root lower bound, and connections with ultrametric fitting.
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BibTeX
@misc{yim2026quantitative,
title = {{A quantitative tree-likeness bound from average hyperbolicity}},
author = {Joon-Hyeok Yim},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.18023},
eprint = {2609.18023},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.18023},
}
RIS
TY - UNPB
TI - A quantitative tree-likeness bound from average hyperbolicity
AU - Joon-Hyeok Yim
PY - 2026
DA - 2026/09/30
PB - arXiv
DO - 10.48550/arxiv.2609.18023
UR - https://arxiv.org/abs/2609.18023
AB - Chatterjee and Sloman proved that a bounded measurable similarity function with sufficiently small average Gromov hyperbolicity admits a tree representation with small mean approximation error. Their argument uses a weighted version of Szemerédi's regularity lemma and does not yield explicit quantitative bounds. Here, we establish a tighter relation between average hyperbolicity and mean tree approximation error. For a similarity function s:S× S→[0,b], we prove that Tree(s) ≤ (63/e)^1/3 √[3]b^2 Hyp(s) ≤ 2.8512 √[3]b^2 Hyp(s). The proof uses a simple pivoting construction inspired by \KwikCluster. We also discuss the optimal dependence on average hyperbolicity, including a square-root lower bound, and connections with ultrametric fitting.
ER -