Abstract
Boesch and McHugh in [J. Combinatorial Theory Ser. B 38 (1985), 1-7] introduced the edge-maximal \((k, \ell )\)-graphs to study of network subcohesion, and obtained best possible upper size bounds for all edge-maximal \((k, \ell )\)-graphs. The best possible lower bounds are obtained in [J. Graph Theory 18 (1994), 227-240]. Let \(k,\ell > 0\) be integers. A strict digraph D is a \((k,\ell )\)-digraph if for any subdigraph H of D, that \(|V(H)|\ge \ell\) implies \(\lambda (H)\le k-1\). An arc-maximal \((k,\ell )\)-digraph D is one such that for any \(e\in A(D^c)\), \(D+e\) is not a \((k,\ell )\)-digraph. We show that there is a close relationship between the extremal edge-maximal \((k,\ell )\)-graphs and the extremal arc-maximal \((k,\ell )\)-digraphs. This is applied to determine the optimal upper and lower bounds of the sizes of an arc-maximal \((k,\ell )\)-digraphs. Moreover, the arc-maximal \((k,\ell )\)-digraphs reaching the lower bounds and the upper bounds are respectively characterized.
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Acknowledgements
The research is supported in part by National Natural Science Foundation of China (11301217, 11861066, 61572010) and Natural Science Foundation of Fujian Province, China (No.2021J01860).
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Xu, L., Lai, HJ., Tian, Y. et al. The Extremal Sizes of Arc-Maximal (k, l)-Digraphs. Graphs and Combinatorics 38, 72 (2022). https://doi.org/10.1007/s00373-022-02468-0
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DOI: https://doi.org/10.1007/s00373-022-02468-0
Keywords
- Maximum subgraph edge-connectivity
- Arc-strong connectivity
- Maximum subdigraph arc-strong connectivity
- \(((k,\, \ell ) )\)-digraphs