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arXiv · 2402.16215

Branch-depth is minor closure of contraction-deletion-depth

Marcin Briański·Daniel Kráľ·Kristýna Pekárková
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Abstract

The notion of branch-depth for matroids was introduced by DeVos, Kwon and Oum as the matroid analogue of the tree-depth of graphs. The contraction-deletion-depth, another tree-depth like parameter of matroids, is the number of recursive steps needed to decompose a matroid by contractions and deletions to single elements. Any matroid with contraction-deletion-depth at most d has branch-depth at most d. However, the two notions are not functionally equivalent as contraction-deletion-depth of matroids with branch-depth two can be arbitrarily large. We show that the two notions are functionally equivalent for representable matroids when minor closures are considered. Namely, an F-representable matroid has small branch-depth if and only if it is a minor of an F-representable matroid with small contraction-deletion-depth. This implies that any class of F-representable matroids has bounded branch-depth if and only if it is a subclass of the minor closure of a class of F-representable matroids with bounded contraction-deletion-depth.

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Marcin Briański, Daniel Kráľ, Kristýna Pekárková. 2024-02-25. Branch-depth is minor closure of contraction-deletion-depth. https://arxiv.org/abs/2402.16215

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