On the signed chromatic number of some classes of graphs

A signed graph (G, sigma) is a graph G along with a function sigma : E(G) -> {+, -}. A closed walk of a signed graph is positive (resp., negative) if it has an even (resp., odd) number of negative edges, counting repetitions. A homomorphism of a (simple) signed graph to another signed graph is a vertex-mapping that preserves adjacencies and signs of closed walks. The signed chromatic number of a signed graph (G, sigma) is the minimum number of vertices vertical bar V (H)vertical bar of a signed graph (H, pi) to which (G, sigma) admits a homomorphism. Homomorphisms of signed graphs have been attracting growing attention in the last decades, especially due to their strong connections to the theories of graph coloring and graph minors. These homomorphisms have been particularly studied through the scope of the signed chromatic number. In this work, we provide new results and bounds on the signed chromatic number of several families of signed graphs (planar graphs, triangle-free planar graphs, K-n-minor-free graphs, and bounded-degree graphs). (C) 2021 Published by Elsevier B.V.