Article in volume
Authors:
Sinan Hu
School of Mathematics and Statistics, Changsha University of Science and Technology
email: husinan7@163.com
Title:
Ramsey numbers for a large tree versus multiple copies of complete graphs of different sizes
PDFSource:
Discussiones Mathematicae Graph Theory 45(2) (2025) 419-429
Received: 2023-10-05 , Revised: 2024-01-16 , Accepted: 2024-01-16 , Available online: 2024-02-02 , https://doi.org/10.7151/dmgt.2537
Abstract:
For two graphs $G$ and $H$, let $G\cup H$ be the union of vertex-disjoint copy
of $G$ and $H$. And the Ramsey number $R(G,H)$ is the minimum integer $N$ such
that any red-blue coloring of the edges of the complete graph $K_N$ contains
either a red copy of $G$ or a blue copy of $H$. If $G$ is connected and
$v(G)\geq s(H)$, it is well known that $R(G,H) \geq (v(G)-1)(\chi(H)-1)+s(H)$,
where $\chi(H)$ is the chromatic number of $H$ and $s(H)$ is the size of the
smallest color class taken over all proper vertex-colorings of $H$ with
$\chi(H)$ colors. Burr defined a connected graph $G$ as $H$-good if the
above inequality becomes equality. In this paper, for integers $t\geq1$ and
$m_{1}\geq m_{2}\geq \cdots\geq m_{t}$, we show that if $n$ is sufficiently
large, then any tree $T_n$ is $\bigcup_{i= 1}^{t}K_{m_{i}}$-good. In particular,
we show that the condition of $n$ being sufficiently large can be relaxed when
$T_n$ is a star.
Keywords:
Ramsey number, tree, Ramsey goodness
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