Small Ramsey Numbers Research Articles

Semidefinite Programming and Ramsey Numbers

Finding exact Ramsey numbers is a problem typically restricted to relatively small graphs. The flag algebra method was developed to find asymptotic results for very large graphs, so it seems that the method is not suitable for finding small Ramsey numbers. But this intuition is wrong, and we will develop a technique to do just that in this paper. We find new upper bounds for many small graph and hypergraph Ramsey numbers. As a result, we prove the exact values $R(K_4^-,K_4^-,K_4^-)=28$, $R(K_8,C_5)= 29$, $R(K_9,C_6)= 41$, $R(Q_3,Q_3)=13$, $R(K_{3,5},K_{1,6})=17$, $R(C_3, C_5, C_5)= 17$, and $R(K_4^-,K_5^-;3)= 12$. We hope that this technique will be adapted to address other questions for smaller graphs with the flag algebra method.

A new construction technique of a triangle-free 3-colored K16’s

In this paper, we propose a new coloring technique of the edges of the complete graph on 16 vertices, K 16, with three different colors, without producing any monochromatic triangle. This method is totally different from those proposed by [R.E. Greenwood, A.M. Gleason, Combinatorial relations and chromatic graphs, Canadian Journal of Mathematics 7 (1955) 1–7; J.G. Kalbfleish, R.G. Stanton, On the maximal triangle-free edge-chromatic graphs in three colors, Journal of Combinatorial Theory 5 (1968) 9–20; C. Laywine, L.P. Mayberry, A simple construction giving the two non-isomorphic triangle free 3-colored K 16’s, Journal of Combinatorial Theory Series B (1988) 120–124; B. Benhamou, Étude des Symétries et de la Cardinalité en Calcul Propoaitionel: Application aux Algorithmes Syntaxiques, Ph.D. Thesis, University of Aix-Marseilles I, France, 1993] which prove that the classical multicolor Ramsey number R(3, 3, 3) is 17. This number is the only non-trivial tricolor Ramsey number known till now in spite of more than fifty years of extensive research on Ramsey numbers [S.P. Radziszowski, Small Ramsey numbers, The Electronic Journal of Combinatorics DS1.Revision 11 (2006) 1–60]. We show also how we can convert the Ramsey-graph 3-coloring problem into a satisfiability instance having 2160 clauses of 3-literals each and 360 variables (i.e., a 3-SAT instance).

On Graphs With Small Ramsey Numbers, II

There exists a constant C such that for every d-degenerate graphs G1 and G2 on n vertices, Ramsey number R(G1,G2) is at most CnΔ, where Δ is the minimum of the maximum degrees of G1 and G2.

On graphs with small Ramsey numbers*

AbstractLet R(G) denote the minimum integer N such that for every bicoloring of the edges of KN, at least one of the monochromatic subgraphs contains G as a subgraph. We show that for every positive integer d and each γ,0 < γ < 1, there exists k = k(d,γ) such that for every bipartite graph G = (W,U;E) with the maximum degree of vertices in W at most d and $|U|\leq |W|^{\gamma }$, $R(G)\leq k|W|$. This answers a question of Trotter. We give also a weaker bound on the Ramsey numbers of graphs whose set of vertices of degree at least d + 1 is independent. © 2001 John Wiley & Sons, Inc. J Graph Theory 37: 198–204, 2001

Some small ramsey numbers

AbstractIn previous work, the Ramsey numbers have been evaluated for all pairs of graphs with at most four points. In the present note, Ramsey numbers are tabulated for pairs F1, F2 of graphs where F1 has at most four points and F2 has exactly five points. Exact results are listed for almost all of these pairs.