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| Natura: | Preprint |
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2024
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| Accesso online: | https://arxiv.org/abs/2409.12404 |
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| _version_ | 1866912838952419328 |
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| author | Fu, Houshan |
| author_facet | Fu, Houshan |
| contents | Jaeger et al. in 1992 introduced group coloring as the dual concept to group connectivity in graphs. Let $A$ be an additive Abelian group, $ f: E(G)\to A$ and $D$ an orientation of a graph $G$. A vertex coloring $c:V(G)\to A$ is an $(A, f)$-coloring if $c(v)-c(u)\ne f(e)$ for each oriented edge $e=uv$ from $u$ to $v$ under $D$. Kochol recently introduced the assigning polynomial to count nowhere-zero chains in graphs--nonhomogeneous analogues of nowhere-zero flows in \cite{Kochol2022}, and later extended the approach to regular matroids in \cite{Kochol2024}. Motivated by Kochol's work, we define the $α$-compatible graph and the cycle-assigning polynomial $P(G, α; k)$ at $k$ in terms of $α$-compatible spanning subgraphs, where $α$ is an assigning of $G$ from its cycles to $\{0,1\}$. We prove that $P(G,α;k)$ evaluates the number of $(A,f)$-colorings of $G$ for any Abelian group $A$ of order $k$ and $f:E(G)\to A$ such that the assigning $α_{D,f}$ given by $f$ equals $α$. Such an assigning is admissible. Based on Kochol's work, we derive that $k^{-c(G)}P(G,α;k)$ is a polynomial enumerating $(A,f)$-tensions and counting specific nowhere-zero chains.
Furthermore, by extending Whitney's broken cycle concept to broken compatible cycles, we show that the absolute value of the coefficient of $k^{|V(G)|-i}$ in $P(G,α;k)$ associated with admissible assignings $α$ equals the number of $α$-compatible spanning subgraphs that have $i$ edges and contain no broken $α$-compatible cycles. According to the combinatorial explanation, we establish a unified order-preserving relation from admissible assignings to cycle-assigning polynomials, and further show that for any admissible assigning $α$ of $G$ with $α(e)=1$ for every loop $e$, the coefficients of $P(G,α;k)$ are nonzero and alternate in sign. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2409_12404 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Polynomials Counting Group Colorings in Graphs Fu, Houshan Combinatorics 05C31, 05C15 Jaeger et al. in 1992 introduced group coloring as the dual concept to group connectivity in graphs. Let $A$ be an additive Abelian group, $ f: E(G)\to A$ and $D$ an orientation of a graph $G$. A vertex coloring $c:V(G)\to A$ is an $(A, f)$-coloring if $c(v)-c(u)\ne f(e)$ for each oriented edge $e=uv$ from $u$ to $v$ under $D$. Kochol recently introduced the assigning polynomial to count nowhere-zero chains in graphs--nonhomogeneous analogues of nowhere-zero flows in \cite{Kochol2022}, and later extended the approach to regular matroids in \cite{Kochol2024}. Motivated by Kochol's work, we define the $α$-compatible graph and the cycle-assigning polynomial $P(G, α; k)$ at $k$ in terms of $α$-compatible spanning subgraphs, where $α$ is an assigning of $G$ from its cycles to $\{0,1\}$. We prove that $P(G,α;k)$ evaluates the number of $(A,f)$-colorings of $G$ for any Abelian group $A$ of order $k$ and $f:E(G)\to A$ such that the assigning $α_{D,f}$ given by $f$ equals $α$. Such an assigning is admissible. Based on Kochol's work, we derive that $k^{-c(G)}P(G,α;k)$ is a polynomial enumerating $(A,f)$-tensions and counting specific nowhere-zero chains. Furthermore, by extending Whitney's broken cycle concept to broken compatible cycles, we show that the absolute value of the coefficient of $k^{|V(G)|-i}$ in $P(G,α;k)$ associated with admissible assignings $α$ equals the number of $α$-compatible spanning subgraphs that have $i$ edges and contain no broken $α$-compatible cycles. According to the combinatorial explanation, we establish a unified order-preserving relation from admissible assignings to cycle-assigning polynomials, and further show that for any admissible assigning $α$ of $G$ with $α(e)=1$ for every loop $e$, the coefficients of $P(G,α;k)$ are nonzero and alternate in sign. |
| title | Polynomials Counting Group Colorings in Graphs |
| topic | Combinatorics 05C31, 05C15 |
| url | https://arxiv.org/abs/2409.12404 |