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arXiv · 2605.18634

Harmonious Colorings: bounds, heuristics and integer-linear formulations

Júlio Araújo·Manoel Campêlo·Beatriz Martins·Marcio C. Santos
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Abstract

A proper coloring $c$ of a simple graph $G$ is harmonious if, for every pair of distinct edges $uv,xy\in E(G)$, we have that $\{c(u),c(v)\}\neq \{c(x),c(y)\}$. The harmonious chromatic number of $G$, denoted by $h(G)$, is the least positive integer $k$ such that $G$ has a harmonious coloring with $k$ colors. In this work, we extend an idea presented in [Kolay, et al. Harmonious coloring: Parameterized algorithms and upper bounds. Theor. Comp. Sci. 772 (2019), 132-142] to compare the harmonious chromatic numbers of two graphs $G$ and $H$, with $H$ being obtained from $G$ by identifying vertices at distance at least three. Furthermore, by fixing a proof presented in the same work, we manage to improve one of its upper bounds. We also introduce and study the first, to the best of our knowledge, integer-linear programming formulations for this problem in the literature, along with some heuristics. We provide some preliminary tests on random instances and instances from the second DIMACS Implementation Challenge.

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Júlio Araújo, Manoel Campêlo, Beatriz Martins, Marcio C. Santos. 2026-05-18. Harmonious Colorings: bounds, heuristics and integer-linear formulations. https://arxiv.org/abs/2605.18634

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