Faber-Krahn Type Inequalities for Trees

The Faber-Krahn theorem states that among all bounded domains with the same volume in ${\mathbb R}^n$ (with the standard Euclidean metric), a ball that has lowest first Dirichlet eigenvalue. Recently it has been shown that a similar result holds for (semi-)regular trees. In this article we show that such a theorem also hold for other classes of (not necessarily non-regular) trees. However, for these new results no couterparts in the world of the Laplace-Beltrami-operator on manifolds are known.Comment: 19 pages, 5 figure

Largest Laplacian Eigenvalue and Degree Sequences of Trees

We investigate the structure of trees that have greatest maximum eigenvalue among all trees with a given degree sequence. We show that in such an extremal tree the degree sequence is non-increasing with respect to an ordering of the vertices that is obtained by breadth-first search. This structure is uniquely determined up to isomorphism. We also show that the maximum eigenvalue in such classes of trees is strictly monotone with respect to majorization.Comment: 9 pages, 2 figure

Graphs with Given Degree Sequence and Maximal Spectral Radius

We describe the structure of those graphs that have largest spectral radius in the class of all connected graphs with a given degree sequence. We show that in such a graph the degree sequence is non-increasing with respect to an ordering of the vertices induced by breadth-first search. For trees the resulting structure is uniquely determined up to isomorphism. We also show that the largest spectral radius in such classes of trees is strictly monotone with respect to majorization.Comment: 12 pages, 4 figures; revised version. Important change: Theorem 3 (formely Theorem 7) now states (and correctly proofs) the majorization result only for "degree sequences of trees" (instead for general connected graphs). Bo Zhou from the South China Normal University in Guangzhou, P.R. China, has found a counter-example to the stronger resul

The first Dirichlet eigenvalue of bicyclic graphs

summary:In this paper, we have investigated some properties of the first Dirichlet eigenvalue of a bicyclic graph with boundary condition. These results can be used to characterize the extremal bicyclic graphs with the smallest first Dirichlet eigenvalue among all the bicyclic graphs with a given graphic bicyclic degree sequence with minor conditions. Moreover, the extremal bicyclic graphs with the smallest first Dirichlet eigenvalue among all the bicycle graphs with fixed $k$ interior vertices of degree at least 3 are obtained

Eigenvectors of the discrete Laplacian on regular graphs - a statistical approach

In an attempt to characterize the structure of eigenvectors of random regular graphs, we investigate the correlations between the components of the eigenvectors associated to different vertices. In addition, we provide numerical observations, suggesting that the eigenvectors follow a Gaussian distribution. Following this assumption, we reconstruct some properties of the nodal structure which were observed in numerical simulations, but were not explained so far. We also show that some statistical properties of the nodal pattern cannot be described in terms of a percolation model, as opposed to the suggested correspondence for eigenvectors of 2 dimensional manifolds.Comment: 28 pages, 11 figure

Geometric representations and symmetries of graphs, maps and other discrete structures and applications in science

Bu proje çalışmasının birinci amacı çizgelerin özdeğer ve özvektör yapılarını çizge özellik ve sabitleri ile ilişkilendirmektir. İkinci amacı biyoloji, bioinformatik, dinamik sistemler, haberleşme, kriptoloji ve sosyal ağlar gibi bir birinden çok farklı alanlardan gelen birbirinden tamamen bağımsız olan temel problemler için çizge kuramı ile özgün modellenmesi ve ortaya çıkan çizge problemlerin çözülmesidir. Üçüncü amacı çizgelerin Castelnuovo-Mumford regülaritesine indirgenmiş eşleşme sayısı ile üstten etkin sınırlar getirmektir.TÜBİTAKPublisher's Versio