New Lower Bounds for Some Multicolored Ramsey Numbers

Abelian Ramsey Length and Asymptotic Lower Bounds

This technical note aims at evaluating an asymptotic lower bound on abelian Ramsey lengths.

Lower bounds for multicolor Ramsey numbers

We give an exponential improvement to the lower bound on diagonal Ramsey numbers for any fixed number of colors greater than two.

An improved lower bound on multicolor Ramsey numbers

A recent breakthrough of Conlon and Ferber yielded an exponential improvement on the lower bounds for multicolor diagonal Ramsey numbers. In this note, we modify their construction and obtain improved bounds for more than three colors.

An improved lower bound for multicolor Ramsey numbers and the half-multiplicity Ramsey number problem

The multicolor Ramsey number problem asks, for each pair of natural numbers $\ell$ and $t$, for the largest $\ell$-coloring of a complete graph with no monochromatic clique of size $t$. Recent works of Conlon-Ferber and Wigderson have improved the longstanding lower bound for this problem. We make a further improvement by replacing an explicit graph appearing in their constructions by a random graph. Graphs useful for this construction are exactly those relevant for a problem of Erdős on graphs with no large cliques and few large independent sets. We also make some basic observations about thi…

A coding perspective on the lower bound for diagonal Ramsey numbers

We give a coding based perspective, on a result of Erdós, on a lower bound for the diagonal ramsey numbers.

Improved Lower Bounds on the Classical Ramsey Numbers R(4,22) and R(4,25)

Circulant graphs have been used to effectively establish lower bounds on many classical Ramsey numbers. Here, we construct circulant graphs of prime order that sharpen the best published lower bounds on two Ramsey numbers. Generalizing previous work in which quadratic and cubic residues were used to construct circulant graphs for the same purpose, we report on the use of quartic and higher-order residues.

A note on lower bounds for hypergraph Ramsey numbers

We improve upon the lower bound for 3-colour hypergraph Ramsey numbers, showing, in the 3-uniform case, that \[r_3 (l,l,l) \geq 2^{l^{c \log \log l}}.\] The old bound, due to Erdős and Hajnal, was \[r_3 (l,l,l) \geq 2^{c l^2 \log^2 l}.\]

New lower bounds for two color and multicolor Ramsey numbers

Using cyclic graphs I give new lower bounds for two color and multicolor Ramsey numbers: R(4,16)>163, R(5,11)>170, R(5,12)>190, R(5,13)>212, R(5,14)>238, R(3,3,9)>117, R(3,3,10)>141 and R(3,3,11)>157. Improving the previous best known bounds.

多色Ramsey下界更新

An update on multicolor Ramsey lower bounds

基于球面随机几何图构造，改进了多色Ramsey数的下界，提供了更精确的理论结果。

有向图的 Mathon 型构造与 Ramsey 数的改进下界

A Mathon-type construction for digraphs and improved lower bounds for Ramsey numbers

本文提出有向图的 Mathon 型构造，证明其与 k 次幂 Paley 有向图的联系，并据此改进多色有向 Ramsey 数的下界。

A Note on Lower Bounds for Induced Ramsey Numbers

We say that a graph $F$ strongly arrows a pair of graphs $(G,H)$ if any 2-colouring of its edges with red and blue leads to either a red $G$ or a blue $H$ appearing as induced subgraphs of $F$. The induced Ramsey number, $IR(G,H)$ is defined as the minimum number of vertices of a graph $F$ which strongly arrows a pair $(G,H)$. We will consider two aspects of induced Ramsey numbers. Firstly there will be shown that the lower bound of the induced Ramsey number for a connected graph $G$ with independence number $α$ and a graph $H$ with clique number $ω$ roughly $\frac{ω^2α}{2}$. This bounds is sh…

Improved lower bound on an Euclidean Ramsey problem

It was previously shown that any two-colour colouring of K(C_n) must contain a monochromatic planar K_4 subgraph for n >= N^*, where 6 <= N^* <= N and N is Graham's number. The bound was later improved to 11 <= N^* <= N. In this article, it is improved to 13 <= N^* <= N.

多色星临界拉姆齐数的下界

Lower Bounds for Multicolor Star-Critical Ramsey Numbers

本文研究多色星临界拉姆齐数，给出其消失的等价判据及非消失时的通用下界，并计算了 $r_*(P_k, P_3, P_3)$，同时证明 $r_*(C_5, P_3)=3$。

An algorithmic framework for obtaining lower bounds for random Ramsey problems

In this paper we introduce a general framework for proving lower bounds for various Ramsey type problems within random settings. The main idea is to view the problem from an algorithmic perspective: we aim at providing an algorithm that finds the desired colouring with high probability. Our framework allows to reduce the probabilistic problem of whether the Ramsey property at hand holds for random (hyper)graphs with edge probability $p$ to a deterministic question of whether there exists a finite graph that forms an obstruction. In the second part of the paper we apply this framework to addres…

Study of Exoo's Lower Bound for Ramsey number $R(5,5)$

We review Exoo's 1989 paper, which demonstrates that a lower bound for the Ramsey number $R(5,5)$ is $43$. We provide an efficient way to verify the claims in the paper, adding detailed proofs. In particular, we replace the reference to computer verification by concise arguments. Using our understanding of the insight behind these proofs, we are also able to analyse variations of the graph constructions to obtain, for example, colourings of $K_{43}$ which have very few monochromatic $K_5$.

Constructive Methods in Gallai-Ramsey Theory for Hypergraphs

Much recent progress in hypergraph Ramsey theory has focused on constructions that lead to lower bounds for the corresponding Ramsey numbers. In this paper, we consider applications of these results to Gallai colorings. That is, we focus on the Ramsey numbers resulting from only considering $t$-colorings of the hyperedges of complete $r$-uniform hypergraphs in which no rainbow $K_{r+1}^{(r)}$-subhypergraphs exists. We also provide new constructions which imply improved lower bounds for many $3$ and $4$-uniform Ramsey numbers and $3$ and $4$-uniform Gallai-Ramsey numbers.

New Lower Bounds for 28 Classical Ramsey Numbers

We establish new lower bounds for $28$ classical two and three color Ramsey numbers, and describe the heuristic search procedures we used. Several of the new three color bounds are derived from the two color constructions; specifically, we were able to use $(5,k)$-colorings to obtain new $(3,3,k)$-colorings, and $(7,k)$-colorings to obtain new $(3,4,k)$-colorings. Some of the other new constructions in the paper are derived from two well-known colorings: the Paley coloring of $K_{101}$ and the cubic coloring of $K_{127}$.

Lower Bound on the Size-Ramsey Number of Tight Paths

The size-Ramsey number $R^{(k)}(H)$ of a $k$-uniform hypergraph $H$ is the minimum number of edges in a $k$-uniform hypergraph $G$ with the property that every `$2$-edge coloring' of $G$ contains a monochromatic copy of $H$. For $k\ge2$ and $n\in\mathbb{N}$, a $k$-uniform tight path on $n$ vertices $P^{(k)}_{n}$ is defined as a $k$-uniform hypergraph on $n$ vertices for which there is an ordering of its vertices such that the edges are all sets of $k$ consecutive vertices with respect to this order. We prove a lower bound on the size-Ramsey number of $k$-uniform tight paths, which is, consider…

Counting monochromatic copies of K_4: a new lower bound for the Ramsey multiplicity problem

Denote by k_4(n) the minimal number of monochromatic copies of a K_4 in a 2-colouring of the edges of K_n and let c_4 := lim k_4(n)/\binom{n}{4}. The best known bounds so far were given by Thomason, who proved that c_4 < 1/33 \approx 0.0303, and Giraud, who showed that c_4 > 1/46 \approx 0.0217. In this paper we prove the new lower bound c_4 > 204603019 / 7112448000 > 0.0287.

Ramsey下界的一个指数性改进

An exponential improvement for Ramsey lower bounds

本文证明了Ramsey数r(ℓ,Cℓ)的下界，展示存在ε>0使得r(ℓ,Cℓ)≥(p_C^{-1/2}+ε)⁠ℓ，其中p_C是满足C=log p_C/log(1-p_C)的唯一解，改进了Erdős在1947年得到的经典下界。

通过精细高斯估计得到更尖锐的拉姆齐下界

Sharper Ramsey lower bounds from refined Gaussian estimates

本文通过精细的累积量生成函数界改进了对角拉姆齐数$R(\ell,C\ell)$的指数下界，对每个固定的$C>1$实现了严格正的指数增益。

Triangular Ramsey Numbers

The purpose of this paper is to introduce the idea of triangular Ramsey numbers and provide values as well as upper and lower bounds for them. To do this, the combinatorial game Mines is introduced; after some necessary theorems about triangular sets are proved. This game is easy enough that young children are able to play. The most basic variations of this game are analyzed and theorems about winning strategies and the existence of draws are proved. The game of Mines is then used to define triangular Ramsey numbers. Lower bounds are found for these triangular Ramsey numbers using the probabil…

Difference Ramsey Numbers and Issai Numbers

We present a recursive algorithm for finding good lower bounds for the classical Ramsey numbers. Using notions from this algorithm we then give some results for generalized Schur numbers, which we call Issai numbers.

New lower bounds for hypergraph Ramsey numbers

The Ramsey number $r_k(s,n)$ is the minimum $N$ such that for every red-blue coloring of the $k$-tuples of $\{1,\ldots, N\}$, there are $s$ integers such that every $k$-tuple among them is red, or $n$ integers such that every $k$-tuple among them is blue. We prove the following new lower bounds for 4-uniform hypergraph Ramsey numbers: $$r_4(5,n) > 2^{n^{c\log n}} \qquad \hbox{ and } \qquad r_4(6,n) > 2^{2^{cn^{1/5}}},$$ where $c$ is an absolute positive constant. This substantially improves the previous best bounds of $2^{n^{c\log\log n}}$ and $2^{n^{c\log n}}$, respectively. Using previously …

New lower bounds on the size-Ramsey number of a path

We prove that for all graphs with at most $(3.75-o(1))n$ edges there exists a 2-coloring of the edges such that every monochromatic path has order less than $n$. This was previously known to be true for graphs with at most $2.5n-7.5$ edges. We also improve on the best-known lower bounds in the $r$-color case.

A lower bound for set-colouring Ramsey numbers

The set-colouring Ramsey number $R_{r,s}(k)$ is defined to be the minimum $n$ such that if each edge of the complete graph $K_n$ is assigned a set of $s$ colours from $\{1,\ldots,r\}$, then one of the colours contains a monochromatic clique of size $k$. The case $s = 1$ is the usual $r$-colour Ramsey number, and the case $s = r - 1$ was studied by Erdős, Hajnal and Rado in 1965, and by Erdős and Szemerédi in 1972. The first significant results for general $s$ were obtained only recently, by Conlon, Fox, He, Mubayi, Suk and Verstraëte, who showed that $R_{r,s}(k) = 2^{Θ(kr)}$ if $s/r$ is bounde…

书图Ramsey数的下界

Lower Bounds for Book Ramsey Numbers

该研究通过块循环构造和SAT求解器，确定了书图Ramsey数的下界，并枚举了临界图数量。

Improved Lower Bounds for Multicolour Ramsey Numbers using SAT-Solvers

This paper sets out the results of a range of searches for linear and cyclic graph colourings with specific Ramsey properties. The new graphs comprise mainly 'template graphs' which can be used in a construction described by the current author in 2021 to build linear or cyclic compound graphs with inherited Ramsey properties. These graphs result in improved lower bounds for a wide range of multicolour Ramsey numbers. Searches were carried out using relatively simple programs (written in the language `C') to generate clauses for input to the PeneLoPe and Plingeling parallel SAT-solvers. When so…

Using the Incompressibility Method to obtain Local Lemma results for Ramsey-type Problems

We reveal a connection between the incompressibility method and the Lovasz local lemma in the context of Ramsey theory. We obtain bounds by repeatedly encoding objects of interest and thereby compressing strings. The method is demonstrated on the example of van der Waerden numbers. It applies to lower bounds of Ramsey numbers, large transitive subtournaments and other Ramsey phenomena as well.

有界度超图的Ramsey下界

Two-color Ramsey lower bounds for bounded degree hypergraphs

研究提出一种k-超图，其最大度不超过Δ，且Ramsey数r(H)达到塔函数级别，推动了Conlon等人2009年问题的进展。

图论的强化学习，II. 小拉姆齐数

Reinforcement learning for graph theory, II. Small Ramsey numbers

本文将 Wagner 的强化学习方法用于搜索小拉姆齐数临界图，给出了多个小拉姆齐数的新下界并改进了 $R(W_5, W_7)$ 的已知下界。

Lower bounds on geometric Ramsey functions

We continue a sequence of recent works studying Ramsey functions for semialgebraic predicates in $\mathbb{R}^d$. A $k$-ary semialgebraic predicate $Φ(x_1,\ldots,x_k)$ on $\mathbb{R}^d$ is a Boolean combination of polynomial equations and inequalities in the $kd$ coordinates of $k$ points $x_1,\ldots,x_k\in\mathbb{R}^d$. A sequence $P=(p_1,\ldots,p_n)$ of points in $\mathbb{R}^d$ is called $Φ$-homogeneous if either $Φ(p_{i_1}, \ldots,p_{i_k})$ holds for all choices $1\le i_1 < \cdots < i_k\le n$, or it holds for no such choice. The Ramsey function $R_Φ(n)$ is the smallest $N$ such that every po…

Ramsey numbers of cubes versus cliques

The cube graph Q_n is the skeleton of the n-dimensional cube. It is an n-regular graph on 2^n vertices. The Ramsey number r(Q_n, K_s) is the minimum N such that every graph of order N contains the cube graph Q_n or an independent set of order s. Burr and Erdos in 1983 asked whether the simple lower bound r(Q_n, K_s) >= (s-1)(2^n - 1)+1 is tight for s fixed and n sufficiently large. We make progress on this problem, obtaining the first upper bound which is within a constant factor of the lower bound.

Ramsey and Gallai-Ramsey numbers for two classes of unicyclic graphs

Given a graph $G$ and a positive integer $k$, define the \emph{Gallai-Ramsey number} to be the minimum number of vertices $n$ such that any $k$-edge coloring of $K_n$ contains either a rainbow (all different colored) triangle or a monochromatic copy of $G$. In this paper, we consider two classes of unicyclic graphs, the star with an extra edge and the path with a triangle at one end. We provide the $2$-color Ramsey numbers for these two classes of graphs and use these to obtain general upper and lower bounds on the Gallai-Ramsey numbers.

Ramsey理论中的一些最新结果

Some recent results in Ramsey theory

本文综述了Ramsey理论中关于Ramsey数的最新突破，包括对角线、近对角线和多色Ramsey数的指数改进，以及诱导Ramsey数的上界结果。

Small minimal $(3, 3)$-Ramsey graphs

We say that $G$ is a $(3, 3)$-Ramsey graph if every $2$-coloring of the edges of $G$ forces a monochromatic triangle. The $(3, 3)$-Ramsey graph $G$ is minimal if $G$ does not contain a proper $(3, 3)$-Ramsey subgraph. In this work we find all minimal $(3, 3)$-Ramsey graphs with up to 13 vertices with the help of a computer, and we obtain some new results for these graphs. We also obtain new upper bounds on the independence number and new lower bounds on the minimum degree of arbitrary $(3, 3)$-Ramsey graphs.

Anti-Ramsey problems in the generalized Petersen graphs for cycles

The anti-Ramsey number $Ar(G,H)$ is the maximum number of colors in an edge-coloring of $G$ with no rainbow copy of $H$. In this paper, we determine the exact anti-Ramsey number in the generalized Petersen graph $P_{n,k}$ for cycles $C_d$, where $1\leq k\leq \lfloor \frac{n-1}{2} \rfloor$ and $5\le d \le 6$. We also give an algorithm to obtain the upper bound or lower bound of anti-Ramsey number.

关于算术雨伞Ramsey性的界限

Bounds on Arithmetic Rainbow Ramsey Multiplicities

本文研究了3色着色下最大化雨伞3项等差数列数量的界限问题，确定了整数模n情况下的上界和下界，并在n为3的倍数时给出了精确最大值。

Ramsey and Gallai-Ramsey numbers for stars with extra independent edges

Given a graph $G$ and a positive integer $k$, define the \emph{Gallai-Ramsey number} to be the minimum number of vertices $n$ such that any $k$-edge coloring of $K_n$ contains either a rainbow (all different colored) triangle or a monochromatic copy of $G$. In this paper, we obtain general upper and lower bounds on the Gallai-Ramsey numbers for the graph $G = S_t^{r}$ obtained from a star of order $t$ by adding $r$ extra independent edges between leaves of the star so there are $r$ triangles and $t - 2r - 1$ pendent edges in $S_t^{r}$. We also prove some sharp results when $t = 2$.

高斯随机图与Ramsey数

Gaussian random graphs and Ramsey numbers

本文通过高斯随机图的构造给出了Ramsey数下界改进的简洁证明，并获得了更优的量化界。

What is Ramsey-equivalent to a clique?

A graph G is Ramsey for H if every two-colouring of the edges of G contains a monochromatic copy of H. Two graphs H and H' are Ramsey-equivalent if every graph G is Ramsey for H if and only if it is Ramsey for H'. In this paper, we study the problem of determining which graphs are Ramsey-equivalent to the complete graph K_k. A famous theorem of Nesetril and Rodl implies that any graph H which is Ramsey-equivalent to K_k must contain K_k. We prove that the only connected graph which is Ramsey-equivalent to K_k is itself. This gives a negative answer to the question of Szabo, Zumstein, and Zurch…

Gallai-Ramsey numbers for books

Given a graph $G$ and a positive integer $k$, the \emph{Gallai-Ramsey number} is defined to be the minimum number of vertices $n$ such that any $k$-edge coloring of $K_n$ contains either a rainbow (all different colored) triangle or a monochromatic copy of $G$. In this paper, we obtain general upper and lower bounds on the Gallai-Ramsey numbers for books $B_{m} = K_{2} + \overline{K_{m}}$ and prove sharp results for $m \leq 5$.

On the Ramsey multiplicity of complete graphs

We show that, for $n$ large, there must exist at least \[\frac{n^t}{C^{(1+o(1))t^2}}\] monochromatic $K_t$s in any two-colouring of the edges of $K_n$, where $C \approx 2.18$ is an explicitly defined constant. The old lower bound, due to Erdős \cite{E62}, and based upon the standard bounds for Ramsey's theorem, is \[\frac{n^t}{4^{(1+o(1))t^2}}.\]

On Berge-Ramsey problems

Given a graph $G$, a hypergraph $\mathcal{H}$ is a Berge copy of $F$ if $V(G)\subset V(\mathcal{H})$ and there is a bijection $f:E(G)\rightarrow E(\mathcal{H})$ such that for any edge $e$ of $G$ we have $e\subset f(e)$. We study Ramsey problems for Berge copies of graphs, i.e. the smallest number of vertices of a complete $r$-uniform hypergraph, such that if we color the hyperedges with $c$ colors, there is a monochromatic Berge copy of $G$. We obtain a couple results regarding these problems. In particular, we determine for which $r$ and $c$ the Ramsey number can be super-linear. We also show…

The oriented size Ramsey number of directed paths

An oriented graph is a directed graph with no bi-directed edges, i.e. if $xy$ is an edge then $yx$ is not an edge. The oriented size Ramsey number of an oriented graph $H$, denoted by $r(H)$, is the minimum $m$ for which there exists an oriented graph $G$ with $m$ edges, such that every $2$-colouring of $G$ contains a monochromatic copy of $H$. In this paper we prove that the oriented size Ramsey number of the directed paths on $n$ vertices satisfies $r(P_n) = Ω(n^2 \log n)$. This improves a lower bound by Ben-Eliezer, Krivelevich and Sudakov. It also matches an upper bound by Bucić and the au…

关于4-团Ramsey-Turán问题的研究

On the Ramsey-Turán problem for 4-cliques

本文在不使用正则性引理的条件下，给出了4-团Ramsey-Turán问题的紧确界，从而大幅扩展了无$K_4$图边数关于独立数函数的紧确界成立范围。

Ramsey upper density of infinite graph factors

The study of upper density problems on Ramsey theory was initiated by Erdős and Galvin in 1993. In this paper we are concerned with the following problem: given a fixed finite graph $F$, what is the largest value of $λ$ such that every 2-edge-coloring of the complete graph on $\mathbb{N}$ contains a monochromatic infinite $F$-factor whose vertex set has upper density at least $λ$? Here we prove a new lower bound for this problem. For some choices of $F$, including cliques and odd cycles, this new bound is sharp, as it matches an older upper bound. For the particular case where $F$ is a triangl…

Gallai-Ramsey numbers for fans

Given a graph $G$ and a positive integer $k$, define the \emph{Gallai-Ramsey number} to be the minimum number of vertices $n$ such that any $k$-edge coloring of $K_n$ contains either a rainbow (all different colored) triangle or a monochromatic copy of $G$. In this paper, we obtain general upper and lower bounds on the Gallai-Ramsey numbers for fans $F_{m} = K_{1} + mK_{2}$ and prove the sharp result for $m = 2$ and for $m = 3$ with $k$ even.

Constructions in Ramsey theory

We provide several constructions for problems in Ramsey theory. First, we prove a superexponential lower bound for the classical 4-uniform Ramsey number $r_4(5,n)$, and the same for the iterated $(k-4)$-fold logarithm of the $k$-uniform version $r_k(k+1,n)$. This is the first improvement of the original exponential lower bound for $r_4(5,n)$ implicit in work of Erd\H os and Hajnal from 1972 and also improves the current best known bounds for larger $k$ due to the authors. Second, we prove an upper bound for the hypergraph Erd\H os-Rogers function $f^k_{k+1, k+2}(N)$ that is an iterated $(k-13)…

递归上界与顶点在线Ramsey游戏的递归上界及其在超图Ramsey数中的应用

Recursive upper bounds for the vertex online Ramsey game with applications to hypergraph Ramsey numbers

本文研究了超图Ramsey数的递归上界，提出改进的递推关系并应用于超图Ramsey数的上界优化。

多色拉姆齐数 $r_k(K_{2, t + 1})$ 的一个新下界

A new lower bound for the multicolor Ramsey number $r_k(K_{2, t + 1})$

本文通过构造素数幂 $t$ 下的无 $K_{2,t+1}$ 图并用于边划分，改进了 $k$ 与 $t$ 为同一素数幂时多色拉姆齐数 $r_k(K_{2,t+1})$ 的下界，得到 $tk^2+1$ 的下界。

关于雏菊的拉姆齐数 II

On the Ramsey number of daisies II

本研究补充了雏菊拉姆齐数的前期结果，得到2色下$(r,m,k)$-雏菊拉姆齐数的$(r-2)$重指数下界，其数量级与完全$r$图拉姆齐数的最优下界相当。

包含中心图的Ramsey数的新界

New bounds for Ramsey numbers involving graphs with a center

本文改进了Chen等人和Mao等人的Ramsey数上界，给出了F_n,F_m和W_n,W_n的新的Ramsey数界，并建立了K_n,K_n的下界和上界，同时提出了一种放大技术来确定轮图与完全图的Ramsey数下界。

Set-coloring Ramsey numbers via codes

For positive integers $n,r,s$ with $r > s$, the set-coloring Ramsey number $R(n;r,s)$ is the minimum $N$ such that if every edge of the complete graph $K_N$ receives a set of $s$ colors from a palette of $r$ colors, then there is guaranteed to be a monochromatic clique on $n$ vertices, that is, a subset of $n$ vertices where all of the edges between them receive a common color. In particular, the case $s=1$ corresponds to the classical multicolor Ramsey number. We prove general upper and lower bounds on $R(n;r,s)$ which imply that $R(n;r,s) = 2^{Θ(nr)}$ if $s/r$ is bounded away from $0$ and $1…