A note on counting flows in signed graphs
| Autor: | DeVos, Matt, Rollová, Edita, Šámal, Robert |
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| Rok vydání: | 2017 |
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| Druh dokumentu: | Working Paper |
| Popis: | Tutte initiated the study of nowhere-zero flows and proved the following fundamental theorem: For every graph $G$ there is a polynomial $f$ so that for every abelian group $\Gamma$ of order $n$, the number of nowhere-zero $\Gamma$-flows in $G$ is $f(n)$. For signed graphs (which have bidirected orientations), the situation is more subtle. For a finite group $\Gamma$, let $\epsilon_2(\Gamma)$ be the largest integer $d$ so that $\Gamma$ has a subgroup isomorphic to $\mathbb{Z}_2^d$. We prove that for every signed graph $G$ and $d \ge 0$ there is a polynomial $f_d$ so that $f_d(n)$ is the number of nowhere-zero $\Gamma$-flows in $G$ for every abelian group $\Gamma$ with $\epsilon_2(\Gamma) = d$ and $|\Gamma| = 2^d n$. Beck and Zaslavsky had previously established the special case of this result when $d=0$ (i.e., when $\Gamma$ has odd order). Comment: 7 pages |
| Databáze: | arXiv |
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