Discrete Morse theory and the topology of matching complexes of complete graphs

Fuente: arXiv
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Hauptverfasser: Mondal, Anupam, Mukherjee, Sajal, Saha, Kuldeep
Format: Preprint
Veröffentlicht: 2023
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author Mondal, Anupam
Mukherjee, Sajal
Saha, Kuldeep
author_facet Mondal, Anupam
Mukherjee, Sajal
Saha, Kuldeep
contents We denote the matching complex of the complete graph with $n$ vertices by $M_n$. Bouc first studied the topological properties of $M_n$ in connection with the Quillen complex. Later Björner, Lovász, Vrećica, and Živaljević showed that $M_n$ is homotopically $(ν_n-1)$-connected, where $ν_n=\lfloor{\frac{n+1}{3}}\rfloor-1$, but in general the topology of $M_n$ is not very well-understood even for smaller natural numbers. Forman developed discrete Morse theory, which has various applications in diverse fields of studies. In this article, we develop a discrete Morse theoretic technique to capture deeper structural topological properties of $M_n$. We show that $M_n$ is \emph{geometrically} $(ν_n-1)$-connected, where the notion of geometrical $k$-connectedness as defined in this article, is stronger than that of homotopical $k$-connectedness. Previously, Björner et al. showed that $M_8$ is simply connected, but not 2-connected. The technique developed here helped us determine that $M_8$ is in fact homotopy equivalent to a wedge of 132 spheres of dimension 2.
format Preprint
id arxiv_https___arxiv_org_abs_2303_07054
institution arXiv
publishDate 2023
record_format arxiv
spellingShingle Discrete Morse theory and the topology of matching complexes of complete graphs
Mondal, Anupam
Mukherjee, Sajal
Saha, Kuldeep
Combinatorics
Algebraic Topology
Geometric Topology
18G85, 57Q70, 05C70, 05E45
We denote the matching complex of the complete graph with $n$ vertices by $M_n$. Bouc first studied the topological properties of $M_n$ in connection with the Quillen complex. Later Björner, Lovász, Vrećica, and Živaljević showed that $M_n$ is homotopically $(ν_n-1)$-connected, where $ν_n=\lfloor{\frac{n+1}{3}}\rfloor-1$, but in general the topology of $M_n$ is not very well-understood even for smaller natural numbers. Forman developed discrete Morse theory, which has various applications in diverse fields of studies. In this article, we develop a discrete Morse theoretic technique to capture deeper structural topological properties of $M_n$. We show that $M_n$ is \emph{geometrically} $(ν_n-1)$-connected, where the notion of geometrical $k$-connectedness as defined in this article, is stronger than that of homotopical $k$-connectedness. Previously, Björner et al. showed that $M_8$ is simply connected, but not 2-connected. The technique developed here helped us determine that $M_8$ is in fact homotopy equivalent to a wedge of 132 spheres of dimension 2.
title Discrete Morse theory and the topology of matching complexes of complete graphs
topic Combinatorics
Algebraic Topology
Geometric Topology
18G85, 57Q70, 05C70, 05E45
url https://arxiv.org/abs/2303.07054