English

Complexity of locally-injective homomorphisms to tournaments

Discrete Mathematics 2023-06-22 v3 Combinatorics

Abstract

For oriented graphs GG and HH, a homomorphism f:GHf: G \rightarrow H is locally-injective if, for every vV(G)v \in V(G), it is injective when restricted to some combination of the in-neighbourhood and out-neighbourhood of vv. Two of the possible definitions of local-injectivity are examined. In each case it is shown that the associated homomorphism problem is NP-complete when HH is a reflexive tournament on three or more vertices with a loop at every vertex, and solvable in polynomial time when HH is a reflexive tournament on two or fewer vertices.

Keywords

Cite

@article{arxiv.1710.08825,
  title  = {Complexity of locally-injective homomorphisms to tournaments},
  author = {Stefan Bard and Thomas Bellitto and Christopher Duffy and Gary MacGillivray and Feiran Yang},
  journal= {arXiv preprint arXiv:1710.08825},
  year   = {2023}
}

Comments

22 pages, 16 figures