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arXiv · 1801.01795

Sparse highly connected spanning subgraphs in dense directed graphs

Dong Yeap Kang
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Abstract

Mader proved that every strongly $k$-connected $n$-vertex digraph contains a strongly $k$-connected spanning subgraph with at most $2kn - 2k^2$ edges, where the equality holds for the complete bipartite digraph ${DK}_{k,n-k}$. For dense strongly $k$-connected digraphs, this upper bound can be significantly improved. More precisely, we prove that every strongly $k$-connected $n$-vertex digraph $D$ contains a strongly $k$-connected spanning subgraph with at most $kn + 800k(k+\overline{\Delta}(D))$ edges, where $\overline{\Delta}(D)$ denotes the maximum degree of the complement of the underlying undirected graph of a digraph $D$. Here, the additional term $800k(k+\overline{\Delta}(D))$ is tight up to multiplicative and additive constants. As a corollary, this implies that every strongly $k$-connected $n$-vertex semicomplete digraph contains a strongly $k$-connected spanning subgraph with at most $kn + 800k^2$ edges, which is essentially optimal since $800k^2$ cannot be reduced to the number less than $k(k-1)/2$. We also prove an analogous result for strongly $k$-arc-connected directed multigraphs. Both proofs yield polynomial-time algorithms.

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Dong Yeap Kang. 2018-01-05. Sparse highly connected spanning subgraphs in dense directed graphs. https://doi.org/10.1017/s0963548318000469

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