AI中文摘要
受Ruzsa-Szemerédi问题的启发,Imolay、Karl、Nagy和Váli研究了Turán数$ex_F(n,G)$的一个变种(称为$G$的$F$-多色Turán数),定义为在$n$个顶点上边不交的$F$拷贝的最大数目,使得不存在$G$的拷贝其边来自不同的$F$拷贝。他们证明,如果不存在从$G$到$F$的同态,则$n^2/v(F)^2+o(n^2)\leq ex_F(n,G)\leq ex(n,G)/e(F)+o(n^2)$,否则$ex_F(n,G)=o(n^2)$。量$ex_F(n,G)$渐近等于$n$顶点$G$-自由图中$F$-打包的最大大小,并且当且仅当$\chi(G)>\chi(F)$时达到上界$ex(n,G)/e(F)+o(n^2)$。 在本文中,我们提供了$ex_F(n,G)$不达到下界$n^2/v(F)^2+o(n^2)$的条件,并通过图爆炸描述了达到该下界的额外图对。特别地,我们证明了对于任意$k\geq 5$,$ex_{C_k(s)}(n,C_{k-2})=n^2/(sk)^2+o(n^2)$及其稳定性。对于退化情形,我们证明如果$\chi(F)=3$且$G$和$F$具有相同的奇围长,则$ex_F(n,G)$满足$(6,3)$型界$n^{2-o(1)}$,推广了Kovács和Nagy的一个结果。我们还证明了对任意满足$\ell>k$的整数$k,\ell$,$ex_{C_{2k+1}}(n,C_{2\ell+1})=O(n^{1+1/\lceil\ell/k\rceil})$,推广了Füredi和Özkahya以及Collier-Cartaino、Graber和Jiang的结果。 此外,我们建立了$ex_{C_4}(n,C_4)=\sqrt{2}n^{3/2}/8+O(n)$。
英文摘要
For graphs $F$ and $G$, $F$-multicolor Turán number of $G$, denoted by $\mathrm{ex}_F(n,G)$, is the maximum number of edge-disjoint copies of $F$ in an $n$-vertex graph such that there is no copy of $G$ whose edges come from distinct copies of $F$. We study this parameter mainly for cycle pairs and determine, up to asymptotic order, when $\mathrm{ex}_{C_k}(n,C_\ell)$ attains the three natural thresholds: the upper bound, the lower bound, and the $n^{2-o(1)}$ regime. In particular, for every odd $k\ge 5$ and every $t\ge 1$, where $C_k(t)$ denotes the $t$-blow-up of $C_k$, we prove $\mathrm{ex}_{C_k(t)}(n,C_{k-2})=n^2/(kt)^2+o(n^2),$ and establish a corresponding stability theorem. We further show that if $F$ and $G$ have the same odd girth $k$ and there exist homomorphisms from both $F$ and $G$ to $C_k$, then $\mathrm{ex}_F(n,G)=n^{2-o(1)}$; in particular, $\mathrm{ex}_{C_k}(n,C_k)=n^{2-o(1)}$ for odd $k$. In addition, we prove $\mathrm{ex}_{C_{2k+1}}(n,C_{2\ell+1})=O\!\left(n^{1+1/\lceil \ell/k\rceil}\right)$ for $\ell>k$ and $\mathrm{ex}_F(n,G)=O(\mathrm{ex}(n,G))$ for bipartite $G$. We particularly establish $\mathrm{ex}_{C_4}(n,C_4)=\frac{\sqrt{2}}{8}n^{3/2}+O(n)$, and give a sufficient condition under which the lower bound cannot be attained.