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Graphs whose Laplacian eigenvalues are almost all 1 or 2

open access: yesSpecial Matrices
We explicitly determine all connected graphs whose Laplacian matrices have at most four eigenvalues different from 1 and 2.
Mohammadian Ali, Xu Shanshan
doaj   +1 more source

Girth and Laplacian eigenvalue distribution

open access: yes
Let $G$ be a connected graph of order $n$ with girth $g$. For $k=1,\dots,\min\{g-1, n-g\}$, let $n(G,k)$ be the number of Laplacian eigenvalues (counting multiplicities) of $G$ that fall inside the interval $[n-g-k+4,n]$. We prove that if $g\ge 4$, then \[ n(G,k)\le n-g. \] Those graphs achieving the bound for $k=1,2$ are determined.
Xu, Leyou, Zhou, Bo
openaire   +2 more sources

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