论文标题

小组连接设置中的许多流动

Many flows in the group connectivity setting

论文作者

DeVos, Matt, Langhede, Rikke, Mohar, Bojan, Šámal, Robert

论文摘要

Two well-known results in the world of nowhere-zero flows are Jaeger's 4-flow theorem asserting that every 4-edge-connected graph has a nowhere-zero $\mathbb{Z}_2 \times \mathbb{Z}_2$-flow and Seymour's 6-flow theorem asserting that every 2-edge-connected graph has a nowhere-zero $ \ mathbb {z} _6 $ -Flow。 Dvořák and the last two authors of this paper extended these results by proving the existence of exponentially many nowhere-zero flows under the same assumptions.我们重新审视此设置,并提供这些结果的扩展和更简单的证明。 在Jaeger,Linial,Payan和Tarsi的重要论文中,零流量的概念扩展到了可选的类型设置。 For a fixed abelian group $Γ$, an oriented graph $G = (V,E)$ is called $Γ$-connected if for every function $f : E \rightarrow Γ$ there is a flow $ϕ: E \rightarrow Γ$ with $ϕ(e) \neq f(e)$ for every $e \in E$ (note that taking $f = 0$ forces $ϕ$ to be nowhere-zero). Jaeger等。证明每个方向的3边缘连接图都是$γ$连接的,只要$ |γ| \ ge 6 $。我们证明,每当$ |γ|时,都有很多解决方案。 \ ge 8 $。对于组$ \ mathbb {z} _6 $,我们证明,对于每个方向的3边缘连接$ g =(v,e)$,with $ \ ell = | e | - | V | \ge 11$ and every $f: E \rightarrow \mathbb{Z}_6$, there are at least $2^{ \sqrt{\ell} / \log \ell}$ flows $ϕ$ with $ϕ(e) \neq f(e)$ for every $e \in E$.

Two well-known results in the world of nowhere-zero flows are Jaeger's 4-flow theorem asserting that every 4-edge-connected graph has a nowhere-zero $\mathbb{Z}_2 \times \mathbb{Z}_2$-flow and Seymour's 6-flow theorem asserting that every 2-edge-connected graph has a nowhere-zero $\mathbb{Z}_6$-flow. Dvořák and the last two authors of this paper extended these results by proving the existence of exponentially many nowhere-zero flows under the same assumptions. We revisit this setting and provide extensions and simpler proofs of these results. The concept of a nowhere-zero flow was extended in a significant paper of Jaeger, Linial, Payan, and Tarsi to a choosability-type setting. For a fixed abelian group $Γ$, an oriented graph $G = (V,E)$ is called $Γ$-connected if for every function $f : E \rightarrow Γ$ there is a flow $ϕ: E \rightarrow Γ$ with $ϕ(e) \neq f(e)$ for every $e \in E$ (note that taking $f = 0$ forces $ϕ$ to be nowhere-zero). Jaeger et al. proved that every oriented 3-edge-connected graph is $Γ$-connected whenever $|Γ| \ge 6$. We prove that there are exponentially many solutions whenever $|Γ| \ge 8$. For the group $\mathbb{Z}_6$ we prove that for every oriented 3-edge-connected $G = (V,E)$ with $\ell = |E| - |V| \ge 11$ and every $f: E \rightarrow \mathbb{Z}_6$, there are at least $2^{ \sqrt{\ell} / \log \ell}$ flows $ϕ$ with $ϕ(e) \neq f(e)$ for every $e \in E$.

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