Longfei Fang

activity

20202026

t

copies of

ℓ

-cycle

2 citations · 5 across the 20 of their papers we have counts for

collaborators

21 papers

math.CO2026

Dense-core approach to the Brualdi--Hoffman--Turán problem on odd wheels

Longfei Fang, Mingqing Zhai, Yuhan Zhang

We present a unified presentation of the fixed-size adjacency-spectral extremal problem for odd wheels $W_{2 k + 1}$ , where $k \geq 2$ and $W_{2 k + 1} = K_{1} \lor C_{2 k}$ . The exceptional cas…

math.CO2026

Edge-spectral supersaturation for tripartite color-critical graphs

Longfei Fang, Huiqiu Lin, Mingqing Zhai

We study edge-spectral supersaturation for two families of color-critical graphs with chromatic number three. For an integer $r \geq 1$ , we define the spectral threshold \[ g_r(m):=…

math.CO2026

Clique supersaturation under a chromatic constraint below the Turán threshold

Benju Wang, Longfei Fang, Jinlong Shu

A central theme in extremal graph theory is the supersaturation problem, which investigates the minimum number of copies of a target subgraph forced by prescribed edge conditions.…

math.CO2026

Counting color-critical subgraphs under Nikiforov's condition

Longfei Fang, Huiqiu Lin, Mingqing Zhai

For a graph $G$ with $m$ edges, let $ρ (G)$ be its spectral radius, and let $N_{F} (G)$ denote the number of copies of $F$ in $G$ . Nikiforov [Combin. Probab.\,Comput., 2002] proved tha…

math.CO2026

More on spectral supersaturation for the bowtie

Longfei Fang, Yongtao Li, Huiqiu Lin

A central topic in extremal graph theory is the supersaturation problem, which studies the minimum number of copies of a fixed substructure that must appear in any graph with more…

math.CO2026

Spectral extremal graphs on closed surfaces of fixed Euler genus

Mingqing Zhai, Longfei Fang, Huiqiu Lin

Graph theory on surfaces extends classical graph structures to topological surfaces, providing a theoretical foundation for characterizing the embedding properties of complex netwo…

math.CO2025

Spectral supersaturation for color-critical graphs

Longfei Fang, Yongtao Li, Huiqiu Lin +1

A graph is color-critical if it contains an edge whose deletion reduces its chromatic number. This class of graphs, including cliques and odd cycles, plays a central role in extrem…

math.CO2025

Non-bipartite graphs without theta subgraphs

Longfei Fang, Huiqiu Lin

Fix a color-critical graph $H$ with $χ (H) = r + 1 \geq 3$ . Simonovits' chromatic critical edge theorem and Nikiforov's spectral chromatic critical edge theorem imply that $T_{n, r}$ is t…

math.CO2025

On the Turán number of odd-ballooning of $3$ -chromatic graphs

Longfei Fang, Xueyi Huang, Huiqiu Lin +1

Given a graph $F$ , the Turán number $ex (n, F)$ is the maximum number of edges in any $n$ -vertex $F$ -free graph. The odd-ballooning of $F$ , denoted by $F^{o}$ , is a graph obtai…

math.CO2025

The spectral Turán problem: Characterizing spectral-consistent graphs

Longfei Fang, Sergey Goryainov, Denis Krotov +2

Let $EX (n, H)$ and $SPEX (n, H)$ denote the families of $n$ -vertex $H$ -free graphs with the maximum size and the maximum spectral radius, respectively. A graph $H$ is said…

math.CO2024

Long cycles and spectral radii in planar graphs

Ping Xu, Huiqiu Lin, Longfei Fang

There is a rich history of studying the existence of cycles in planar graphs. The famous Tutte theorem on the Hamilton cycle states that every 4-connected planar graph contains a H…

math.CO2024

Turán numbers for non-bipartite graphs and applications to spectral extremal problems

Longfei Fang, Michael Tait, Mingqing Zhai

Given a graph family $H$ with $min_{H \in H} χ (H) = r + 1 \geq 3$ . Let $ex (n, H)$ and $spex (n, H)$ be the maximum number of edges and th…

math.CO2024★ 2 cited

Extremal eigenvalues with respect to graph minors

Mingqing Zhai, Longfei Fang, Huiqiu Lin

Let $s p e x (n, H_{min or})$ denote the maximum spectral radius of $n$ -vertex $H$ -minor free graphs. The problem on determining this extremal value can be dated back to the early 1990s.…

math.CO2024

Spectral extremal results on trees

Longfei Fang, Huiqiu Lin, Jinlong Shu +1

Let $spex (n, F)$ be the maximum spectral radius over all $F$ -free graphs of order $n$ , and $SPEX (n, F)$ be the family of $F$ -free graphs of order $n$ with spectral radius…

math.CO2023

Spectral extremal results on edge blow-up of graphs

Longfei Fang, Huiqiu Lin

Let $ex (n, F)$ and $spex (n, F)$ be the maximum size and maximum spectral radius of an $F$ -free graph of order $n$ , respectively. The value $spex (n, F)$ is called the…

math.CO2023

Spectral extremal problem on the square of $ℓ$ -cycle

Longfei Fang, Yanhua Zhao

Let $C_{ℓ}$ be the cycle of order $ℓ$ . The square of $C_{ℓ}$ , denoted by $C_{ℓ}^{2}$ , is obtained by joining all pairs of vertices with distance no more than two in $C_…

math.CO2023

Extremal spectral results of planar graphs without vertex-disjoint cycles

Longfei Fang, Huiqiu Lin, Yongtang Shi

Given a planar graph family $F$ , let $ex_{P} (n, F)$ and $spex_{P} (n, F)$ be the maximum size and maximum spectral radius…

math.CO2023★ 2 cited

Spectral extremal problem on $t$ copies of $ℓ$ -cycle

Longfei Fang, Mingqing Zhai, Huiqiu Lin

Denote by $t C_{ℓ}$ the disjoint union of $t$ cycles of length $ℓ$ . Let $e x (n, F)$ and $s p e x (n, F)$ be the maximum size and spectral radius over all $n$ -vertex $F$ -free graphs, re…

math.CO2021★ 1 cited

Outerplanar Turán numbers of cycles and paths

Longfei Fang, Mingqing Zhai

A graph is outerplanar if it can be embedded in a plane such that all vertices lie on its outer face. The outerplanar Turán number of a given graph $H$ , denoted by ${\rm ex}_{\math…

math.CO2020

Planar Turán Number of intersecting triangles

Longfei Fang, Mingqing Zhai, Bing Wang

The planar Turán number of a given graph $H$ , denoted by $e x_{P} (n, H)$ , is the maximum number of edges over all planar graphs on $n$ vertices that do not contain a copy o…

math.SP2020

The maximum number of s-cliques in connected graphs and its application to spectral moment

Longfei Fang, Mingqing Zhai, Bing Wang

Extremal problems concerning the number of complete subgraphs have a long story in extremal graph theory. Let $k_{s} (G)$ be the number of $s$ -cliques in a graph $G$ and $m={{r_m}\cho…

Dense-core approach to the Brualdi--Hoffman--Turán problem on odd wheels

Edge-spectral supersaturation for tripartite color-critical graphs

Clique supersaturation under a chromatic constraint below the Turán threshold

Counting color-critical subgraphs under Nikiforov's condition

More on spectral supersaturation for the bowtie

Spectral extremal graphs on closed surfaces of fixed Euler genus

Spectral supersaturation for color-critical graphs

Non-bipartite graphs without theta subgraphs

On the Turán number of odd-ballooning of 3-chromatic graphs

The spectral Turán problem: Characterizing spectral-consistent graphs

Long cycles and spectral radii in planar graphs

Turán numbers for non-bipartite graphs and applications to spectral extremal problems

Extremal eigenvalues with respect to graph minors

Spectral extremal results on trees

Spectral extremal results on edge blow-up of graphs

Spectral extremal problem on the square of ℓ-cycle

Extremal spectral results of planar graphs without vertex-disjoint cycles

Spectral extremal problem on t copies of ℓ-cycle

Outerplanar Turán numbers of cycles and paths

Planar Turán Number of intersecting triangles

The maximum number of s-cliques in connected graphs and its application to spectral moment

On the Turán number of odd-ballooning of $3$ -chromatic graphs

Spectral extremal problem on the square of $ℓ$ -cycle

Spectral extremal problem on $t$ copies of $ℓ$ -cycle