Harmonious Colorings: bounds, heuristics and integer-linear formulations

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Main Authors: Araújo, Júlio, Campêlo, Manoel, Martins, Beatriz, Santos, Marcio C.
Format: Preprint
Published: 2026
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author Araújo, Júlio
Campêlo, Manoel
Martins, Beatriz
Santos, Marcio C.
author_facet Araújo, Júlio
Campêlo, Manoel
Martins, Beatriz
Santos, Marcio C.
contents 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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id arxiv_https___arxiv_org_abs_2605_18634
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publishDate 2026
record_format arxiv
spellingShingle Harmonious Colorings: bounds, heuristics and integer-linear formulations
Araújo, Júlio
Campêlo, Manoel
Martins, Beatriz
Santos, Marcio C.
Combinatorics
Discrete Mathematics
68R10
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.
title Harmonious Colorings: bounds, heuristics and integer-linear formulations
topic Combinatorics
Discrete Mathematics
68R10
url https://arxiv.org/abs/2605.18634