2015/07/16 by Thomas Schweser, Schweser, Thomas, Michael Stiebitz +1
Mathematics · #Combinatorics (math.CO) #FOS: Mathematics #math.CO
paper · pdf · doi:10.48550/arxiv.1507.04569
21 pages
arxiv created 2015/07/16 · arxiv updated 2015/07/17
A signed graph is a graph in which each edge is labeled with +1 or -1. A (proper) vertex coloring of a signed graph is a mapping \f that assigns to each vertex v∈ V(G) a color \f(v)∈ \mz such that every edge vw of G satisfies \f(v)\not= \sg(vw)\f(w), where \sg(vw) is the sign of the edge vw. For an integer h≥ 0, let \Ga2h=\±1,±2, …, ± h\ and \Ga2h+1=\Ga2h ∪ \0\. Following \citeMaRS2015, the signed chromatic number \scn(G) of G is the least integer k such that G admits a vertex coloring \f with \rm im(\f)⊆ \Gak. As proved in \citeMaRS2015, every signed graph G satisfies \scn(G)≤ \De(G)+1 and there are three types of signed connected simple graphs for which equality holds. We will extend this Brooks' type result by considering graphs having multiple edges. We will also proof a list version of this result by characterizing degree choosable signed graphs. Furthermore, we will establish some basic facts about color critical signed graphs.