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math.CO2026

An exponentially small gap of the Perron vector on independent sets

Hongzhang Chen, Jianxi Li, Yongtao Li +2

A classical result of Cioabă states that if is a connected graph with the unit Perron vector , then any independent set of satisfies $\sum_{v\in S} x_v^2 \l…

math.CO2026

An Improved Interpolation Theorem and Disproofs of Two Conjectures on 2-Connected Subgraphs

Haiyang Liu, Bo Ning

We prove that any \(2\)-connected graph \(G\) on \(n\) vertices with minimum degree \(δ(G) \ge \frac{n}{4}+2\) contains a \(2\)-connected subgraph of order \(k\) for every integer…

math.CO2025

Exact Turán numbers of two vertex-disjoint paths

Miao Dong, Bo Ning, Long-Tu Yuan +1

The Turán number of a graph is the maximum number of edges in any graph of order that does not contain as a subgraph. In 1959, Erd\H os and Gallai obtained a sharp uppe…

math.CO2025

Two conjectures on vertex-disjoint rainbow triangles

Xu Liu, Bo Ning, Yuting Tian

In 1963, Dirac proved that every -vertex graph has vertex-disjoint triangles if and minimum degree . The base case can be reduced t…

math.CO2025

A new spectral Turán theorem for weighted graphs and consequences

Lele Liu, Bo Ning

Confirming a conjecture of Elphick and Edwards and strengthening a spectral theorem of Wilf, Nikiforov proved that for any -free graph , , wh…

math.CO2025

The stability of independence polynomials of complete bipartite graphs

Guo Chen, Bo Ning, Jianhua Tu

The independence polynomial of a graph is termed {\it stable} if all its roots are located in the left half-plane , and the graph itse…