Eigenvalues of the Laplacian Matrices of Cycles with One Overweighted Edge
摘要
We study the individual behavior of the eigenvalues of the laplacian matrices of the cyclic graph of order n, where one edge has weight \(\alpha \in \mathbb {C}\) , with \(\operatorname {Re}(\alpha )>1\) , and all the others have weights 1. This paper is a sequel to two previous ones where we considered \(\operatorname {Re}(\alpha ) \in [0,1]\) and \(\operatorname {Re}(\alpha )<0\) . Now, we prove that for \(\operatorname {Re}(\alpha )>1\) and \(n > \operatorname {Re}(\alpha )/\operatorname {Re}(\alpha -1)\) , one eigenvalue is greater than 4 while the others belong to \([0,4]\) and are distributed as the function \(x\mapsto 4\sin ^2(x/2)\) . Additionally, we prove that as n tends to \(\infty \) , the outlier eigenvalue converges exponentially to \(4\operatorname {Re}(\alpha )^2/(2\operatorname {Re}(\alpha )-1)\) . We give exact formulas for half of the inner eigenvalues, while for the others we justify the convergence of Newton’s method and the fixed-point iteration method. We find asymptotic expansions, as n tends to \(\infty \) , both for the eigenvalues belonging to \([0,4]\) and the outliers. We also compute the eigenvectors and their norms.