Combinatorics and Graph Theory

On a Seven-Vertex Directed Graph with Universalclosed-Walk Weights and Integral Jordan Structure

Authors: Peilin Wen

We investigate a 7-vertex strongly connected directed graph whose adjacency matrix A exhibits an exceptionally clean algebraic structure. The characteristic polynomial factorises completely as χA(λ) = λ2 (λ −2)(λ −1)(λ + 1)3 ,so the spectrum is {2, 1, −1, 0} with algebraic multiplicities 1, 1, 3, 2, respectively. The Perron root is ρ(A) = 2, and the associated right eigenvector isv = (9, 3, 2, 6, 7, 1, 8)T∈Z7 >0.For every directed edge i →j we define the rational weight wij = vj/(2vi). These weights form a row-stochastic matrix. We prove that for any closed directed walk of length L (vertices and edges may repeat), the product of the weights along the walk is exactly 2−L , independent of the walk’s itinerary. The proof follows solely from the Perron eigenvector equation and the elementary in—out balance of vertices along a closed walk. We further show that A is non-diagonalisable: it contains a 2 × 2 Jordan block for λ = 0 and at least one for λ = −1. The one-dimensional nullspace is spanned by (1, −1, 0, 0, −1, 1, 0)T , encoding a linear conservation law among four vertices. This graph provides a minimal exactly solvable model with potential applications to loop-model partition functions, non-Hermitian quantum walks, and rapidly mixing Markov chains.Keywords: directed graph; closed walk; Perron—Frobenius theorem; Jordan canonical form; row-stochastic matrix; non-Hermitian quantum walk; exceptional point; exactly solvable model.

Comments: 9 Pages.

Download: PDF

Submission history

[v1] 2026-06-29 19:53:17

Unique-IP document downloads: 44 times

ai.Vixra.org is a AI assisted e-print repository rather than a journal. Articles hosted may not yet have been verified by peer-review and should be treated as preliminary. In particular, anything that appears to include financial or legal advice or proposed medical treatments should be treated with due caution. ai.Vixra.org will not be responsible for any consequences of actions that result from any form of use of any documents on this website.

Add your own feedback and questions here:
You are equally welcome to be positive or negative about any paper but please be polite. If you are being critical you must mention at least one specific error, otherwise your comment will be deleted as unhelpful.