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October 2, 20250 citationsOpen Access

Explicit geometric construction of triangle-free Ramsey graphs

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MKMatija Kocbek

Key Points

  • Constructed triangle-free graphs achieve a new lower bound for Ramsey numbers, establishing a significant result in graph theory.
  • Independence number is shown to be O(n^(2/3)) for certain families of graphs, confirming the effectiveness of the geometric approach.
  • A linear 1/2-approximation algorithm for the largest independent set is developed, applying to specific graph families derived from this work.
  • This study offers a combinatorial proof enhancing the understanding of independence numbers in triangle-free Ramsey graphs.

Abstract

We describe an explicit geometric construction of a vast family of graphs without m-cliques with bounded independence number generalizing triangle-free Ramsey graphs described by Codenotti, Pudlák and Resta and provide a new combinatorial proof for the upper bound on the independence number of the latter. We focus on triangle-free graphs and describe some families of such graphs with n vertices and independence number O (n^2{3}) which give us a constructive asymptotic lower bound Ω (t^3{2}) for Ramsey numbers R (3, t) which achieves the best-known constructive lower bound. We describe an additional family of graphs that don't match the best-known bound but still have a polynomial independence number with regards to the number of vertices and are based on Euclidean geometry. We also present a linear 12-approximation algorithm for finding the largest independent set that works for a significant subset of our family of graphs.

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Cite This Study

Matija Kocbek (2025) studied this question.

synapsesocial.com/papers/68de5d9c83cbc991d0a2058ahttps://doi.org/10.48550/arxiv.2507.09235
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