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arXiv · 1204.2568

A bivariate chromatic polynomial for signed graphs

Matthias Beck·Mela Hardin
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Abstract

We study Dohmen--P\"onitz--Tittmann's bivariate chromatic polynomial $c_\Gamma(k,l)$ which counts all $(k+l)$-colorings of a graph $\Gamma$ such that adjacent vertices get different colors if they are $\le k$. Our first contribution is an extension of $c_\Gamma(k,l)$ to signed graphs, for which we obtain an inclusion--exclusion formula and several special evaluations giving rise, e.g., to polynomials that encode balanced subgraphs. Our second goal is to derive combinatorial reciprocity theorems for $c_\Gamma(k,l)$ and its signed-graph analogues, reminiscent of Stanley's reciprocity theorem linking chromatic polynomials to acyclic orientations.

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Matthias Beck, Mela Hardin. 2012-04-11. A bivariate chromatic polynomial for signed graphs. https://arxiv.org/abs/1204.2568

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