All Questions
Tagged with extremal-graph-theory ramsey-theory
14 questions
15
votes
4
answers
639
views
Sets of points containing permutations - a Ramsey-type question
The following question arised as a side-question in a geometric problem. It has a "feel" similar to problems in Ramsey-theory, but I have not found any mention of it (also I'm not very familiar with ...
- 711
11
votes
1
answer
396
views
Dense triangle-free graphs and their independent sets
Recall that a graph is triangle-free if it does not contain a copy of $K_3$. Also, for a graph $G$, $\alpha(G)$ shall denote its independence number. Lastly, we will write $o(1)$ to denote quantities ...
- 3,499
7
votes
2
answers
362
views
Reference request: monochromatic paths in edge-colored complete graphs
Given $k,c \in \mathbb{N}$, let $P(k,c)$ be the minimum $n$ such that no matter how we color the edges of the complete graph $K_n$ with $c$ colors, there is always a monochromatic path of length $k$.
...
- 71
6
votes
2
answers
317
views
Is there a graph that is Ramsey for $P_{2n}$ but is $C_{2n+1}-$free
Write $F\to G$ to mean that for every two coloring of the edges of $F$, there exists a monochromatic copy of $G$. Nešetřil and Rödl proved that for every graph $G$, there exists a graph $F$ such that ...
- 61
6
votes
0
answers
108
views
What is the smallest number of vertices in a graph whose every orientation contains a directed straight path of length 3
For a graph $\Gamma$ and a digraph $\vec H$ we write $\Gamma\Rightarrow \vec H$ if any orientation of $\Gamma$ contains an isometric and isomorphic copy of the digraph $\vec H$. Since each graph ...
- 42k
4
votes
1
answer
230
views
Independence number of $C_4$-free graphs
It's well known that a $C_4$-free graph of order $n$ has average degree $O(\sqrt{n})$, and it follows that the independence number is $\Omega(\sqrt{n})$.
This bound cannot be improved over $\Theta(n^{\...
- 9,501
4
votes
2
answers
2k
views
The number of monochromatic triangles
It is well known that the minimum number of monochromatic triangles in a red/blue coloring of the edges of the complete graph $K_n$ is given by Goodman's formula
$$M(n)=\binom n3-\left\lfloor\frac n2\...
- 13.4k
4
votes
0
answers
113
views
What properties do graphs avoiding large regular subgraphs have?
Fix a positive integer $r$ and real $\delta \in (0,1)$.
Let $G$ be an undirected graph on $n$ vertices. Suppose that $G$ does not contain an $r$-regular subgraph on at least $\delta n$ vertices (i.e., ...
- 557
3
votes
2
answers
276
views
Ramsey-Turán density function is well defined
Define
$$RT(n,K_l,f(n))=ex_l(n,f(n))=\max_G\{e(G): K_l \not\subset G, v(G)=n, \alpha(G)\leq f(n)\}$$
and the Ramsey-Turán density function $f_l:(0,1] \to \mathbb{R}$ as
$$f_l(\alpha)=\lim_{n\to \infty}...
- 227
2
votes
1
answer
482
views
Suppose the independent number of a graph is bounded. How small the clique number can be?
Suppose the independent number of a graph is bounded. How small the clique number can be? linear?
It seems to be a natural problem to ask. but I could not find any reference.
Thanks.
- 23
2
votes
0
answers
134
views
Even cycle constrained edge coloring
Is minimum colors needed to assign colors to edges of complete graph $K_n$ so that every $2t$ simple cycle where $t\in\Big\{1,\dots,2\Big\lfloor\frac{n}2\Big\rfloor\Big\}$ contains atleast $t+1$ ...
- 13.9k
1
vote
1
answer
175
views
Distribution of Induced Subgraphs of Extremal Ramsey Graphs
Choose $k$. Let $G = (V,E)$ be a graph on $n = R(k,k)-1$ vertices (that is, $G$ is an extremal example for $R(k,k)$, and $g : E \to \{r, b\}$ be an edge 2-coloring such that there is no monochromatic $...
- 316
1
vote
1
answer
159
views
Acyclic partition of edges in tournaments
The following question is related to a research problem I am working on. I am curious if anyone is aware of a solution, if there are similar problems which may aid me in finding a solution, or if the ...
- 13
0
votes
0
answers
153
views
A Non-trivial intersecting set system problem
Liven large enough $k\in\Bbb N$ fix $m\in\{2,3,\dots,k\}$ and fix $4k$ cardinality set $K_{4k}$.
What is the maximum $n\in\Bbb N$ such that at some $t\geq2n-1$ there are $$\mbox{ subsets }L_1,L_2,\...
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