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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

A Nordhaus-Gaddum Type Problem for the Normalized Laplacian Spectrum and Graph Cheeger Constant

Knudson, Adam Widtsoe 21 June 2024 (has links) (PDF)
We will study various quantities related to connectivity of a graph. To this end, we look at Nordhaus-Gaddum type problems, which are problems where the same quantity is studied for a graph $G$ and its complement $G^c$ at the same time. For a graph $G$ on $n$ vertices with normalized Laplacian eigenvalues $0 = \lambda_1(G) \leq \lambda_2(G) \leq \cdots \leq \lambda_n(G)$ and graph complement $G^c$, we prove that \begin{equation*} \max\{\lambda_2(G),\lambda_2(G^c)\}\geq \frac{2}{n^2}. \end{equation*} We do this by way of lower bounding $\max\{i(G), i(G^c)\}$ and $\max\{h(G), h(G^c)\}$ where $i(G)$ and $h(G)$ denote the isoperimetric number and Cheeger constant of $G$, respectively. We also discuss some related Nordhaus-Gaddum questions.

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