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arXiv 1907.04559math.CO
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$K_r$的最大长度-Bootstrap渗滤

The maximum length of $K_r$-Bootstrap Percolation

József Balogh, Gal Kronenberg, Alexey Pokrovskiy, Tibor Szabó

摘要:

图引导渗流,也称为弱饱和,是由Bollobás在1968年提出的。在这个过程中,我们从初始的“感染”边集$E_0$开始,并根据预定的规则感染新的边。给定一个图$H$和一组先前感染的边$E_t\subseteq E(K_n)$,如果未感染的边$e$在$G=([n],E_t\cup e)$中完成了一个新的$H$拷贝,则它将被感染。Bollobás提出的一个问题是,进程在稳定之前可以运行的最长时间。Bollobás,Przykucki,Riordan和Sahasrabudhe认为这个问题的最自然的情况下,$H=K_r$。他们回答了$r\leq 4$的问题,并给出了每个$r\geq 5$的非平凡下界。他们还证明,对于每个整数$r$,最大运行时间是$o(n^2)$。本文对每个$r\geq 6$证明了他们的猜想,并给出了$r=5$的一个更好的下界,证明中使用了Behrend构造.

英文摘要:

Graph-bootstrap percolation, also known as weak saturation, was introduced by Bollobás in 1968. In this process, we start with initial "infected" set of edges $E_0$, and we infect new edges according to a predetermined rule. Given a graph $H$ and a set of previously infected edges $E_t\subseteq E(K_n)$, we infect a non-infected edge $e$ if it completes a new copy of $H$ in $G=([n],E_t\cup e)$. A question raised by Bollobás asks for the maximum time the process can run before it stabilizes. Bollobás, Przykucki, Riordan, and Sahasrabudhe considered this problem for the most natural case where $H=K_r$. They answered the question for $r\leq 4$ and gave a non-trivial lower bound for every $r\geq 5$. They also conjectured that the maximal running time is $o(n^2)$ for every integer $r$. In this paper we disprove their conjecture for every $r\geq 6$ and we give a better lower bound for the case $r=5$; in the proof we use the Behrend construction.

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