,
Benjamin Moseley
,
Heather Newman
Creative Commons Attribution 4.0 International license
The π_p-norm objectives for correlation clustering present a fundamental trade-off between minimizing total disagreements (the πβ-norm) and ensuring fairness to individual nodes (the π_β-norm). Surprisingly, in the offline setting it is possible to simultaneously approximate all π_p-norms with a single clustering. Can this powerful guarantee be achieved in an online setting? This paper provides the first affirmative answer. We present a single algorithm for the online-with-a-sample (AOS) model that, given a small constant fraction of the input as a sample, produces one clustering that is simultaneously O(logβ΄ n)-competitive for all π_p-norms with high probability, O(log n)-competitive for the π_β-norm with high probability, and O(1)-competitive for the πβ-norm in expectation. This work successfully translates the offline "all-norm" guarantee to the online world.
Our setting is motivated by a new hardness result that demonstrates a fundamental separation between these objectives in the standard random-order (RO) online model. Namely, while the πβ-norm is trivially O(1)-approximable in the RO model, we prove that any algorithm in the RO model for the fairness-promoting π_β-norm must have a competitive ratio of at least Ξ©(n^{1/3}). This highlights the necessity of a different beyond-worst-case model. We complement our algorithm with lower bounds, showing our competitive ratios for the πβ- and π_β- norms are nearly tight in the AOS model.
@InProceedings{davies_et_al:LIPIcs.ICALP.2026.73,
author = {Davies, Sami and Moseley, Benjamin and Newman, Heather},
title = {{Online Correlation Clustering: Simultaneously Optimizing All π\underlinep-Norms}},
booktitle = {53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)},
pages = {73:1--73:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-428-4},
ISSN = {1868-8969},
year = {2026},
volume = {374},
editor = {Bhattacharya, Sayan and Nanongkai, Danupon and Benedikt, Michael and Puppis, Gabriele},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2026.73},
URN = {urn:nbn:de:0030-drops-264620},
doi = {10.4230/LIPIcs.ICALP.2026.73},
annote = {Keywords: Online algorithms, correlation clustering, all-norms objective, beyond-worst-case analysis}
}