,
Nick Gravin
,
Tristan Pollner,
Aviad Rubinstein
,
Hongao Wang
,
S. Matthew Weinberg
,
Qianfan Zhang
Creative Commons Attribution 4.0 International license
We investigate prophet inequalities with competitive ratios approaching 1, seeking to generalize k-uniform matroids. We first show that large girth does not suffice: for all k, there exists a matroid of girth ≥ k and a prophet inequality instance on that matroid whose optimal competitive ratio is 1/2. Next, we show k-fold matroid unions do suffice: we provide a prophet inequality with competitive ratio 1-O(√{(log k)/k}) for any k-fold matroid union. Our prophet inequality follows from an online contention resolution scheme.
The key technical ingredient in our online contention resolution scheme is a novel bicriterion concentration inequality for arbitrary monotone 1-Lipschitz functions over independent items which may be of independent interest. Applied to our particular setting, our bicriterion concentration inequality yields "Chernoff-strength" concentration for a 1-Lipschitz function that is not (approximately) self-bounding.
@InProceedings{alon_et_al:LIPIcs.ITCS.2025.4,
author = {Alon, Noga and Gravin, Nick and Pollner, Tristan and Rubinstein, Aviad and Wang, Hongao and Weinberg, S. Matthew and Zhang, Qianfan},
title = {{A Bicriterion Concentration Inequality and Prophet Inequalities for k-Fold Matroid Unions}},
booktitle = {16th Innovations in Theoretical Computer Science Conference (ITCS 2025)},
pages = {4:1--4:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-361-4},
ISSN = {1868-8969},
year = {2025},
volume = {325},
editor = {Meka, Raghu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2025.4},
URN = {urn:nbn:de:0030-drops-226329},
doi = {10.4230/LIPIcs.ITCS.2025.4},
annote = {Keywords: Prophet Inequalities, Online Contention Resolution Schemes, Concentration Inequalities}
}