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arXiv 1603.04724math.CO
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关于给定图的分解阈值

On the decomposition threshold of a given graph

Stefan Glock, Daniela Kühn, Allan Lo, Richard Montgomery, Deryk Osthus

摘要:

研究了给定图$F$的$F$分解阈值$δ_F$.图$G$的$F$ -分解是图$G$中的$F$的边不相交副本的集合,它们一起覆盖$G$的每条边。(Such只有当$G$是$F$ -可除的,即,如果$e(F)\mid e(G)$和$G$的每个顶点度可以被表示为$F$的顶点度的线性组合,$F$ -分解才可以存在。$F$ -分解阈值$δ_F$是确保具有$δ(G)\ge(δ_F+o(1))n$的$n$顶点上的$F$ -可分图$G$具有$F$ -分解的最小值。我们的主要结果意味着以下对于一个给定的图$F$,其中$δ_F^\ast$是$δ_F$和$χ:=χ(F)$的分数版本:(i)$δ_F\le \max\{δ_F^\ast,1-1/(χ+1)\}$ ;(ii)如果$χ\ge 5$,那么$δ_F\in\{δ_F^{\ast},1-1/χ,1-1/(χ+1)\}$ ;(iii)我们确定$δ_F$,如果$F$是二部的。特别地,(i)意味着$δ_{K_r}=δ^\ast_{K_r}$ .我们的证明涉及最近的“迭代”吸收方法的进一步发展。

英文摘要:

We study the $F$-decomposition threshold $δ_F$ for a given graph $F$. Here an $F$-decomposition of a graph $G$ is a collection of edge-disjoint copies of $F$ in $G$ which together cover every edge of $G$. (Such an $F$-decomposition can only exist if $G$ is $F$-divisible, i.e. if $e(F)\mid e(G)$ and each vertex degree of $G$ can be expressed as a linear combination of the vertex degrees of $F$.) The $F$-decomposition threshold $δ_F$ is the smallest value ensuring that an $F$-divisible graph $G$ on $n$ vertices with $δ(G)\ge(δ_F+o(1))n$ has an $F$-decomposition. Our main results imply the following for a given graph $F$, where $δ_F^\ast$ is the fractional version of $δ_F$ and $χ:=χ(F)$: (i) $δ_F\le \max\{δ_F^\ast,1-1/(χ+1)\}$; (ii) if $χ\ge 5$, then $δ_F\in\{δ_F^{\ast},1-1/χ,1-1/(χ+1)\}$; (iii) we determine $δ_F$ if $F$ is bipartite. In particular, (i) implies that $δ_{K_r}=δ^\ast_{K_r}$. Our proof involves further developments of the recent `iterative' absorbing approach.

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