Pseudo-Twins and Isomorphic Subgraphs

Presenters/Authors

Hua Wang, Georgia Southern UniversityFollow
Stephan Wagner, Georgia Southern University

Document Type

Presentation

Presentation Date

3-24-2012

Abstract or Description

We show that a number of graph invariants are, even combined, insufficient to distinguish between nonisomorphic trees or general graphs. Among these are: the set of eigenvalues (equivalently, the characteristic polynomial), the number of independent sets of all sizes or the number of connected subgraphs of all sizes. We therefore extend the classical theorem of Schwenk that almost every tree has a cospectral mate, and we provide an answer to a question of Jamison on average subtree orders of trees. The simple construction that we apply for this purpose is based on finding graphs with two distinguished vertices (called pseudo-twins) that do not belong to the same orbit but whose removal yields isomorphic graphs.

Sponsorship/Conference/Institution

Southeastern-Atlantic Sectional Meeting of the Society for Industrial and Applied Mathematics (SIAM-SEAS)

Location

Huntsville, AL

Recommended Citation

Wang, Hua, Stephan Wagner. 2012. "Pseudo-Twins and Isomorphic Subgraphs." Department of Mathematical Sciences Faculty Presentations. Presentation 494.
https://digitalcommons.georgiasouthern.edu/math-sci-facpres/494