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| Main Authors: | , , |
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| Format: | Preprint |
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2024
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| Online Access: | https://arxiv.org/abs/2409.09634 |
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| _version_ | 1866916394448191488 |
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| author | Fu, Houshan Ren, Xiangyu Wang, Suijie |
| author_facet | Fu, Houshan Ren, Xiangyu Wang, Suijie |
| contents | Kochol introduced the assigning polynomial $F(G,α;k)$ to count nowhere-zero $(A,b)$-flows of a graph $G$, where $A$ is a finite Abelian group and $α$ is a $\{0,1\}$-assigning from a family $Λ(G)$ of certain nonempty vertex subsets of $G$ to $\{0,1\}$. We introduce the concepts of $b$-compatible graph and $b$-compatible broken bond to give an explicit formula for the assigning polynomials and to examine their coefficients. More specifically, for a function $b:V(G)\to A$, let $α_{G,b}$ be a $\{0,1\}$-assigning of $G$ such that for each $X\inΛ(G)$, $α_{G,b}(X)=0$ if and only if $\sum_{v\in X}b(v)=0$. We show that for any $\{0,1\}$-assigning $α$ of $G$, if there exists a function $b:V(G)\to A$ such that $G$ is $b$-compatible and $α=α_{G,b}$, then the assigning polynomial $F(G,α;k)$ has the $b$-compatible spanning subgraph expansion \[ F(G,α;k)=\sum_{\substack{S\subseteq E(G),\\G-S\mbox{ is $b$-compatible}}}(-1)^{|S|}k^{m(G-S)}, \] and is the following form $F(G,α;k)=\sum_{i=0}^{m(G)}(-1)^ia_i(G,α)k^{m(G)-i}$, where each $a_i(G,α)$ is the number of subsets $S$ of $E(G)$ having $i$ edges such that $G-S$ is $b$-compatible and $S$ contains no $b$-compatible broken bonds with respect to a total order on $E(G)$. Applying the counting interpretation, we also obtain unified comparison relations for the signless coefficients of assigning polynomials. Namely, for any $\{0,1\}$-assignings $α,α'$ of $G$, if there exist functions $b:V(G)\to A$ and $b':V(G)\to A'$ such that $G$ is both $b$-compatible and $b'$-compatible, $α=α_{G,b}$, $α'=α_{G,b'}$ and $α(X)\leα'(X)$ for all $X\inΛ(G)$, then \[ a_i(G,α)\le a_i(G,α') \quad \mbox{ for }\quad i=0,1,\ldots, m(G). \] |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2409_09634 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Counting Flows of $b$-compatible Graphs Fu, Houshan Ren, Xiangyu Wang, Suijie Combinatorics 05C31, 05C21 Kochol introduced the assigning polynomial $F(G,α;k)$ to count nowhere-zero $(A,b)$-flows of a graph $G$, where $A$ is a finite Abelian group and $α$ is a $\{0,1\}$-assigning from a family $Λ(G)$ of certain nonempty vertex subsets of $G$ to $\{0,1\}$. We introduce the concepts of $b$-compatible graph and $b$-compatible broken bond to give an explicit formula for the assigning polynomials and to examine their coefficients. More specifically, for a function $b:V(G)\to A$, let $α_{G,b}$ be a $\{0,1\}$-assigning of $G$ such that for each $X\inΛ(G)$, $α_{G,b}(X)=0$ if and only if $\sum_{v\in X}b(v)=0$. We show that for any $\{0,1\}$-assigning $α$ of $G$, if there exists a function $b:V(G)\to A$ such that $G$ is $b$-compatible and $α=α_{G,b}$, then the assigning polynomial $F(G,α;k)$ has the $b$-compatible spanning subgraph expansion \[ F(G,α;k)=\sum_{\substack{S\subseteq E(G),\\G-S\mbox{ is $b$-compatible}}}(-1)^{|S|}k^{m(G-S)}, \] and is the following form $F(G,α;k)=\sum_{i=0}^{m(G)}(-1)^ia_i(G,α)k^{m(G)-i}$, where each $a_i(G,α)$ is the number of subsets $S$ of $E(G)$ having $i$ edges such that $G-S$ is $b$-compatible and $S$ contains no $b$-compatible broken bonds with respect to a total order on $E(G)$. Applying the counting interpretation, we also obtain unified comparison relations for the signless coefficients of assigning polynomials. Namely, for any $\{0,1\}$-assignings $α,α'$ of $G$, if there exist functions $b:V(G)\to A$ and $b':V(G)\to A'$ such that $G$ is both $b$-compatible and $b'$-compatible, $α=α_{G,b}$, $α'=α_{G,b'}$ and $α(X)\leα'(X)$ for all $X\inΛ(G)$, then \[ a_i(G,α)\le a_i(G,α') \quad \mbox{ for }\quad i=0,1,\ldots, m(G). \] |
| title | Counting Flows of $b$-compatible Graphs |
| topic | Combinatorics 05C31, 05C21 |
| url | https://arxiv.org/abs/2409.09634 |