arXiv subjects

Susu Wang

Publications and source records attributed to Susu Wang.

4 recordsLinked to original sources

arXiv2026

Reconfiguration graphs of $K_{2,3}$-minor-free graphs

The $\ell$-reconfiguration graph of a graph $G$, denoted by $\mathcal{R}_{\ell}(G)$, is the graph whose vertices are the proper $\ell$-colorings of $G$, with an edge between two colorings if they differ in color on exactly one vertex. For any graph $G$ of treewidth at most $2$, Bousquet and Perarnau showed that $\mathcal{R}_\ell(G)$ has linear diameter for $\ell\geq 6$. This result was later extended by Bartier, Bousquet, and Heinrich, who proved that $\mathcal{R}_5(G)$ also has linear diameter. In this paper, we show that for each $\ell\geq 5$, the $\ell$-reconfiguration graphs of $K_{2,3}$-minor-free graphs, some of which include graphs of treewidth $3$, have linear diameter. As a key step in our proof, we also establish that the $(\ell-1)$-reconfiguration graphs of cactus graphs have linear diameter.

math.CO↗

arXiv2024

Reconfiguration graphs for vertex colorings of $P_5$-free graphs

For any positive integer $k$, the reconfiguration graph for all $k$-colorings of a graph $G$, denoted by $\mathcal{R}_k(G)$, is the graph where vertices represent the $k$-colorings of $G$, and two $k$-colorings are joined by an edge if they differ in color on exactly one vertex. Bonamy et al. established that for any $2$-chromatic $P_5$-free graph $G$, $\mathcal{R}_k(G)$ is connected for each $k\geq 3$. On the other hand, Feghali and Merkel proved the existence of a $7p$-chromatic $P_5$-free graph $G$ for every positive integer $p$, such that $\mathcal{R}_{8p}(G)$ is disconnected. In this paper, we offer a detailed classification of the connectivity of $\mathcal{R} _k(G) $ concerning $t$-chromatic $P_5$-free graphs $G$ for cases $t=3$, and $t\geq4$ with $t+1\leq k \leq {t\choose2}$. We demonstrate that $\mathcal{R}_k(G)$ remains connected for each $3$-chromatic $P_5$-free graph $G$ and each $k \geq 4$. Furthermore, for each $t\geq4$ and $t+1 \leq k \leq {t\choose2}$, we provide a construction of a $t$-chromatic $P_5$-free graph $G$ with $\mathcal{R}_k(G)$ being disconnected. This resolves a question posed by Feghali and Merkel.

math.CO↗

arXiv2024

Global stability and period-doubling bifurcations of a discrete Kolmogorov predator-prey model with Ricker-type prey growth

In this paper, we study the dynamics of a discrete Kolmogorov predator-prey model with Ricker-type prey growth. We give the sufficient and necessary condition to guarantee the existence and uniqueness of the positive fixed point. Using the center manifold theory, we prove that the period-doubling bifurcations can occur at the positive fixed point. Furthermore, our numerical simulations reveal that the model can exhibit cascades of period-doubling bifurcations leading to chaos, which is a significant difference from the behavior of continuous predator-prey models. Despite the complexities of the model dynamics, we are able to provide a criterion for the global stability of the positive fixed point by using a geometric analysis of the nullclines.

math.DS↗

arXiv2022

Some Mader-perfect graph classes

The dichromatic number of $D$, denoted by $\overrightarrowχ(D)$, is the smallest integer $k$ such that $D$ admits an acyclic $k$-coloring. We use $mader_{\overrightarrowχ}(F)$ to denote the smallest integer $k$ such that if $\overrightarrowχ(D)\ge k$, then $D$ contains a subdivision of $F$. A digraph $F$ is called Mader-perfect if for every subdigraph $F'$ of $F$, ${\rm mader }_{\overrightarrowχ}(F')=|V(F')|$. We extend octi digraphs to a larger class of digraphs and prove that it is Mader-perfect, which generalizes a result of Gishboliner, Steiner and Szabó [Dichromatic number and forced subdivisions, {\it J. Comb. Theory, Ser. B} {\bf 153} (2022) 1--30]. We also show that if $K$ is a proper subdigraph of $\overleftrightarrow{C_4}$ except for the digraph obtained from $\overleftrightarrow{C_4}$ by deleting an arbitrary arc, then $K$ is Mader-perfect.

math.CO↗