English

A Dirac-type theorem for arbitrary Hamiltonian $H$-linked digraphs

Combinatorics 2025-03-27 v3

Abstract

Given any digraph DD on nn vertices, let P(D)\mathcal{P}(D) be the family of all directed paths in DD, and let HH be a digraph with the arc set A(H)={a1,,ak}A(H)=\{a_1, \ldots, a_k\}. The digraph DD is called arbitrary Hamiltonian HH-linked if for any injective map f:V(H)V(D)f: V(H)\rightarrow V(D) and any integer set N={n1,,nk}\mathcal{N}=\{n_1, \ldots, n_k\} satisfying that ni4n_i\geq4 for each i{1,,k}i\in\{1, \ldots, k\}, there is a map g:A(H)P(D)g: A(H)\rightarrow \mathcal{P}(D) such that for every arc ai=uva_i=uv, g(ai)g(a_i) is a directed path from f(u)f(u) to f(v)f(v) of length nin_i, and different arcs are mapped into internally vertex-disjoint directed paths in DD, and i[k]V(g(ai))=V(D)\bigcup_{i\in[k]}V(g(a_i))=V(D). Here, the length of a directed path is defined as the number of its arcs. In this paper, we prove that for any digraph HH with kk arcs and δ(H)1\delta(H)\geq1, there exists a constant C0=C0(k)C_0=C_0(k) such that if DD is a digraph of order nC0n\geq C_0 and minimum in- and out-degree at least n/2+kn/2+k, then it is arbitrary Hamiltonian HH-linked. The lower bound on the minimum in- and out-degree is best possible. We further prove a more general form that allows kk to be linear in nn, while imposing some restrictions on the lengths of the subdivided arcs. As corollaries, we solved a conjecture of Wang \cite{Wang} for sufficiently large graphs, and partly answered a problem raised by Pavez-Sign\'{e} \cite{Pavez}.

Keywords

Cite

@article{arxiv.2401.17475,
  title  = {A Dirac-type theorem for arbitrary Hamiltonian $H$-linked digraphs},
  author = {Yangyang Cheng and Zhilan Wang and Jin Yan},
  journal= {arXiv preprint arXiv:2401.17475},
  year   = {2025}
}
R2 v1 2026-06-28T14:32:32.064Z