On the DP-chromatic Number of Cartesian Products of Critical Graphs
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| Format: | Preprint |
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2025
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| _version_ | 1866908470669737984 |
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| author | Kaul, Hemanshu Mudrock, Jeffrey A. Sharma, Gunjan |
| author_facet | Kaul, Hemanshu Mudrock, Jeffrey A. Sharma, Gunjan |
| contents | DP-coloring (also called correspondence coloring) is a well-studied generalization of list coloring introduced by Dvořák and Postle in 2015. The following sharp bound on the DP-chromatic number of the Cartesian product of graphs $G$ and $H$ is known: $χ_{DP}(G \square H) \leq \text{min}\{χ_{DP}(G) + \text{col}(H), χ_{DP}(H) + \text{col}(G) \} - 1$ where $χ_{DP}(G)$ is the DP-chromatic number of $G$ and $\text{col}(H)$ is the coloring number of $H$. We seek to understand when $χ_{DP}(G \square K_{l,t})$ is far from its chromatic number: $χ(G \square K_{l,t}) = \max \{χ(G), 2 \}$ in the case that $G$ is a $k$-critical graph with $χ_{DP}(G)=k$. In particular, we have $χ_{DP}(G \square K_{l,t}) \leq k + l$, and for fixed $l$ we wish to find the smallest $t$ for which this upper bound is achieved. This can be viewed as an extension of the classic result that the list chromatic number of $K_{l,t}$ is $l+1$ if and only if $t \geq l^l$. Our results illustrate that the DP color function of $G$, the DP analogue of the chromatic polynomial, provides a concept and tool that is useful for making progress on this problem. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2507_21421 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | On the DP-chromatic Number of Cartesian Products of Critical Graphs Kaul, Hemanshu Mudrock, Jeffrey A. Sharma, Gunjan Combinatorics 05C15, 05C30, 05C69 DP-coloring (also called correspondence coloring) is a well-studied generalization of list coloring introduced by Dvořák and Postle in 2015. The following sharp bound on the DP-chromatic number of the Cartesian product of graphs $G$ and $H$ is known: $χ_{DP}(G \square H) \leq \text{min}\{χ_{DP}(G) + \text{col}(H), χ_{DP}(H) + \text{col}(G) \} - 1$ where $χ_{DP}(G)$ is the DP-chromatic number of $G$ and $\text{col}(H)$ is the coloring number of $H$. We seek to understand when $χ_{DP}(G \square K_{l,t})$ is far from its chromatic number: $χ(G \square K_{l,t}) = \max \{χ(G), 2 \}$ in the case that $G$ is a $k$-critical graph with $χ_{DP}(G)=k$. In particular, we have $χ_{DP}(G \square K_{l,t}) \leq k + l$, and for fixed $l$ we wish to find the smallest $t$ for which this upper bound is achieved. This can be viewed as an extension of the classic result that the list chromatic number of $K_{l,t}$ is $l+1$ if and only if $t \geq l^l$. Our results illustrate that the DP color function of $G$, the DP analogue of the chromatic polynomial, provides a concept and tool that is useful for making progress on this problem. |
| title | On the DP-chromatic Number of Cartesian Products of Critical Graphs |
| topic | Combinatorics 05C15, 05C30, 05C69 |
| url | https://arxiv.org/abs/2507.21421 |