Graded Betti numbers of a hyperedge ideal associated to join of graphs
Abstract
Let $G$ be a finite simple graph on the vertex set $V(G)$ and let $r$ be a positive integer. We consider the hypergraph $\mathrm{Con}_r(G)$ whose vertices are the vertices of $G$ and the (hyper)edges are all $A\subseteq V(G)$ such that $|A|=r+1$ and the induced subgraph $G[A]$ is connected. The (hyper)edge ideal $I_r(G)$ of $\mathrm{Con}_r(G)$ is also the Stanley-Reisner ideal of a generalisation of the independence complex of $G$, called the $r$-independence complex $\mathrm{Ind}_r(G)$. In this article we make extensive use of the Mayer-Vietoris sequence to find the graded Betti numbers of $I_r(G_1*G_2)$ in terms of the graded Betti numbers of $I_r(G_1)$ and $I_r(G_2)$, where $G_1*G_2$ is the join of $G_1$ and $G_2$. Moreover, we find formulas for all the graded Betti numbers of $I_r(G)$, when $G$ is a complete graph, complete multipartite graph, cycle graph and the wheel graph.
- Publication:
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arXiv e-prints
- Pub Date:
- November 2023
- DOI:
- 10.48550/arXiv.2311.07308
- arXiv:
- arXiv:2311.07308
- Bibcode:
- 2023arXiv231107308K
- Keywords:
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- Mathematics - Commutative Algebra;
- Mathematics - Combinatorics;
- 13F55;
- 05E45
- E-Print:
- Comments are welcome!