The absolute values of the perfect matching derangement graph's eigenvalues almost follow the lexicographic order of partitions

Abstract

In 2013, Ku and Wong showed that for any partitions $\mu$ and $\mu'$ of a positive integer $n$ with the same first part $u$ and the lexicographic order $\mu\triangleleft \mu'$, the eigenvalues $\xi_{\mu}$ and $\xi_{\mu'}$ of the derangement graph $\Gamma_n$ have the property $|\xi_{\mu}|\le |\xi_{\mu'}|$, where the equality holds if and only if $u=3$ and all other parts are less than $3$. In this article, we obtain an analogous conclusion on the eigenvalues of the perfect matching derangement graph $\mathcal{M}_{2n}$ of $K_{2n}$ by finding a new recurrence formula for the eigenvalues of $\mathcal{M}_{2n}$.