Exact Sequences for the Homology of the Matching Complex

Abstract

Building on work by Bouc and by Shareshian and Wachs, we provide a toolbox of long exact sequences for the reduced simplicial homology of the matching complex $M_n$, which is the simplicial complex of matchings in the complete graph $K_n$. Combining these sequences in different ways, we prove several results about the 3-torsion part of the homology of $M_n$. First, we demonstrate that there is nonvanishing 3-torsion in $H_d(M_n;Z)$ whenever $ν_n \le d \le (n-6}/2$, where ${\nu }_n=\lceil (n-4)/3\rceil$. By results due to Bouc and to Shareshian and Wachs, $H_{{\nu }_n}(M_n;Z)$ is a nontrivial elementary 3-group for almost all $n$ and the bottom nonvanishing homology group of $M_n$ for all $n\ne 2$. Second, we prove that $H_d(M_n;Z)$ is a nontrivial 3-group whenever ${\nu }_n\le d\le (2n-9)/5$. Third, for each $k\ge 0$, we show that there is a polynomial $f_k(r)$ of degree 3k such that the dimension of $H_{k-1+r}(M_{2k+1+3r};Z_3)$, viewed as a vector space over $Z_3$, is at most $f_k(r)$ for all $r\ge k+2$.

31 pages

References in corpus (1)

• Five-Torsion in the Homology of the Matching Complex on 14 Vertices

Cited by in corpus (10)

• Representation stability for syzygies of line bundles on Segre--Veronese varieties
• More Torsion in the Homology of the Matching Complex
• Five-Torsion in the Homology of the Matching Complex on 14 Vertices
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• Gorenstein and Cohen-Macaulay Matching Complexes
• Generalized chessboard complexes and discrete Morse theory
• The commuting complex of the symmetric group with bounded number of $p$-cycles
• On the 3-torsion Part of the Homology of the Chessboard Complex
• Top homology of hypergraph matching complexes, $p$-cycle complexes and Quillen complexes of symmetric groups
• Decision trees, monotone functions, and semimatroids