On Minimizing the Maximum Color for the 1-2-3 Conjecture

Julien Bensmail (1) , Bi Li (2) , Binlong Li (3) , Nicolas Nisse (1)

1 COATI - Combinatorics, Optimization and Algorithms for Telecommunications
2 Xidian University
3 NPU - Northwestern Polytechnical University [Xi'an]

The 1-2-3 Conjecture asserts that, for every connected graph different from K2 , its edges can be labeled with 1,2,3 so that, when coloring each vertex with the sum of its incident labels, no two adjacent vertices get the same color. This conjecture takes place in the more general context of distinguishing labelings, where the goal is to label graphs so that some pairs of their elements are distinguishable relatively to some parameter computed from the labeling. In this work, we investigate the consequences of labeling graphs as in the 1-2-3 Conjecture when it is further required to make the maximum resulting color as small as possible. In some sense, we aim at producing a number of colors that is as close as possible to the chromatic number of the graph. We first investigate the hardness of determining the minimum maximum color by a labeling for a given graph, which we show is NP-complete in the class of bipartite graphs but polynomial-time solvable in the class of graphs with bounded treewidth. We then provide bounds on the minimum maximum color that can be generated both in the general context, and for particular classes of graphs. Finally, we study how using larger labels permits to reduce the maximum color.

Mots clés: edge labelings; proper vertex-colorings; 1-2-3 Conjecture; small vertex colors

Domaines: Mathématique discrète [cs.DM]

Julien Bensmail, Bi Li, Binlong Li, Nicolas Nisse. On Minimizing the Maximum Color for the 1-2-3 Conjecture. [Research Report] université côte d'azur. 2019. ⟨hal-02330418v1⟩