The maximum spectral radius of connected graphs with prescribed order and size

In 1986, Brualdi and Solheid asked which connected graph of prescribed order and size has maximum adjacency spectral radius. We complete the classification for every feasible pair of parameters. We prove that no graph outside the dense and star threshold families is extremal, including at ties, and settle the range $n\le e+1$, where the star candidate is not defined. The final comparison \emph{between} the dense and star candidates is supplied by Damnjanović's Propositions~4.1--4.2, not reproved here. We combine an exact Bellman recursion with dense-core domination, fractional complete-split bounds, and a virtual-star inequality. Three remaining comparison families (J), (K1), and (K2) are established analytically and by exact polynomial and Sturm certificates. The exact certificates are implemented in Python/SymPy and SageMath.

Authors

Publication Details

Journal
arXiv (Cornell University)
Published
2026-10-26
DOI
https://doi.org/10.48550/arxiv.2610.34905
Primary Topic
Graph theory and applications
Type
preprint
Controls
|||
ALL TIME
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
preprint

The maximum spectral radius of connected graphs with prescribed order and size

Dragan Stevanović
arXiv (Cornell University)
Graph theory and applications
preprint

The maximum spectral radius of connected graphs with prescribed order and size

Dragan Stevanović
preprint en

Abstract

In 1986, Brualdi and Solheid asked which connected graph of prescribed order and size has maximum adjacency spectral radius. We complete the classification for every feasible pair of parameters. We prove that no graph outside the dense and star threshold families is extremal, including at ties, and settle the range $n\le e+1$, where the star candidate is not defined. The final comparison \emph{between} the dense and star candidates is supplied by Damnjanović's Propositions~4.1--4.2, not reproved here. We combine an exact Bellman recursion with dense-core domination, fractional complete-split bounds, and a virtual-star inequality. Three remaining comparison families (J), (K1), and (K2) are established analytically and by exact polynomial and Sturm certificates. The exact certificates are implemented in Python/SymPy and SageMath.

arXiv (Cornell University)
Graph theory and applications
AI Navigator

Ask Laika to Summarize, Analyze, and Connect papers live on the map.

Summarize Papers & Methodologies

Extract key findings, datasets, and comparative methods across publications.

Benchmark Rankings & Visual Analytics

Rank top research institutions, authors, funders, topics, and journals by Field-Weighted Citation Impact (FWCI) and paper volume with instant charts.

Connect Distant Disciplines

Bridge topological clusters on the map to find hidden collaborative intersections.

Laika access coming soon