English

Orientations of graphs omitting non-edge-critical directed graphs

Combinatorics 2025-04-04 v2

Abstract

In 1974, Erd\H{o}s asked the following question: given a graph GG and a directed graph H\vec{H}, how many ways are there to orient the edges of GG such that it does not contain H\vec{H} as a subgraph? We denote this value by D(G,H)D(G, \vec{H}). Further, we let D(n,H)D(n, \vec{H}) denote the maximum of D(G,H)D(G, \vec{H}) over all graphs GG on nn vertices. In 2006, Alon and Yuster gave an exact answer when H\vec{H} is a tournament. In 2023, Buci\'c, Janzer, and Sudakov gave asymptotic answers for all directed graphs H\vec{H}, and in the same paper, they gave an exact answer when H\vec{H} is a directed cycle. In this paper, we give a better bound for some specific non-bipartite directed graphs. Further, we obtain exact values of D(G,H)D(G, \vec{H}) for some small non-edge-critical directed graphs H\vec{H}. Finally, for these graphs, we classify all graphs GG that attain the bound D(G,H)=D(n,H)D(G, \vec{H}) = D(n, \vec{H}).

Keywords

Cite

@article{arxiv.2502.21287,
  title  = {Orientations of graphs omitting non-edge-critical directed graphs},
  author = {Hannah Sheats},
  journal= {arXiv preprint arXiv:2502.21287},
  year   = {2025}
}

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34 pages