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A Logarithmic Approximation of Linearly-Ordered Colourings
Authors
Johan Håstad 
,
Björn Martinsson ,
Tamio-Vesa Nakajima ,
Stanislav Živný
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Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques (APPROX/RANDOM 2024)
Series: Leibniz International Proceedings in Informatics (LIPIcs)
Conference: International Conference on Approximation Algorithms for Combinatorial Optimization Problems (APPROX) - License:
Creative Commons Attribution 4.0 International license
- Publication Date: 2024-09-16
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Acknowledgements
This paper is a merger of independent work by Håstad and Martinsson, and by Nakajima and Živný respectively. We are grateful to Venkat Guruswami for noting and informing the authors of the fact that we independently had found the same algorithm.
Cite AsGet BibTex
Johan Håstad, Björn Martinsson, Tamio-Vesa Nakajima, and Stanislav Živný. A Logarithmic Approximation of Linearly-Ordered Colourings. In Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques (APPROX/RANDOM 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 317, pp. 7:1-7:6, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
https://doi.org/10.4230/LIPIcs.APPROX/RANDOM.2024.7
https://doi.org/10.4230/LIPIcs.APPROX/RANDOM.2024.7
Abstract
A linearly ordered (LO) k-colouring of a hypergraph assigns to each vertex a colour from the set {0,1,…,k-1} in such a way that each hyperedge has a unique maximum element. Barto, Batistelli, and Berg conjectured that it is NP-hard to find an LO k-colouring of an LO 2-colourable 3-uniform hypergraph for any constant k ≥ 2 [STACS'21] but even the case k = 3 is still open. Nakajima and Živný gave polynomial-time algorithms for finding, given an LO 2-colourable 3-uniform hypergraph, an LO colouring with O^*(√n) colours [ICALP'22] and an LO colouring with O^*(n^(1/3)) colours [ACM ToCT'23]. Very recently, Louis, Newman, and Ray gave an SDP-based algorithm with O^*(n^(1/5)) colours. We present two simple polynomial-time algorithms that find an LO colouring with O(log₂(n)) colours, which is an exponential improvement.
Subject Classification
ACM Subject Classification
- Theory of computation → Approximation algorithms analysis
- Theory of computation → Constraint and logic programming
Keywords
- Linear ordered colouring
- Hypergraph
- Approximation
- Promise Constraint Satisfaction Problems
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References
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