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Wyszukujesz frazę "Wang, Ligong" wg kryterium: Autor


Wyświetlanie 1-5 z 5
Tytuł:
Deficiency and Forbidden Subgraphs of Connected, Locally-Connected Graphs
Autorzy:
Li, Xihe
Wang, Ligong
Powiązania:
https://bibliotekanauki.pl/articles/32083830.pdf
Data publikacji:
2020-02-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
05C40
05C70
Opis:
A graph $G$ is locally-connected if the neighbourhood $ N_G (v) $ induces a connected subgraph for each vertex $v$ in $G$. For a graph $G$, the deficiency of $G$ is the number of vertices unsaturated by a maximum matching, denoted by $ \text{def} (G) $. In fact, the deficiency of a graph measures how far a maximum matching is from being perfect matching. Saito and Xiong have studied subgraphs, the absence of which forces a connected and locally-connected graph $G$ of sufficiently large order to satisfy $ \text{def} (G) \le 1 $. In this paper, we extend this result to the condition of $ \text{def} (G) \le k $, where k is a positive integer. Let $ \beta_0 = \ceil{ 1/2 (3+\sqrt{8k+17} ) } −1 $, we show that $ K_{1,2}, K_{1,3}, . . ., K_{1,β_0}, K_3 $ or \( K_2 \lor 2K_1 \) is the required forbidden subgraph. Furthermore, we obtain some similar results about 3-connected, locally-connected graphs. Key Words: deficiency, locally-connected graph, matching, forbidden subgraph.
Źródło:
Discussiones Mathematicae Graph Theory; 2020, 40, 1; 195-208
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Gallai-Ramsey Numbers for Rainbow $S_3^+$ and Monochromatic Paths
Autorzy:
Li, Xihe
Wang, Ligong
Powiązania:
https://bibliotekanauki.pl/articles/32387979.pdf
Data publikacji:
2022-05-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
Gallai-Ramsey number
rainbow coloring
monochromatic paths
Opis:
Motivated by Ramsey theory and other rainbow-coloring-related problems, we consider edge-colorings of complete graphs without rainbow copy of some fixed subgraphs. Given two graphs $G$ and $H$, the $k$-colored Gallai-Ramsey number $ gr_k(G : H)$ is defined to be the minimum positive integer $n$ such that every $k$-coloring of the complete graph on $n$ vertices contains either a rainbow copy of $G$ or a monochromatic copy of $H$. Let $ S_3^+$ be the graph on four vertices consisting of a triangle with a pendant edge. In this paper, we prove that $ gr_k(S_3^+ : P_5) = k+4 (k \ge 5)$, $ gr_k(S_3^+ : mP_2) = (m-1)k+m+1 (k \ge 1) $, $ gr_k(S_3^+ : P_3 \cup P_2) = k+4 (k \ge 5) $ and $ gr_k( S_3^+ : 2P_3) = k+5 (k \ge1) $.
Źródło:
Discussiones Mathematicae Graph Theory; 2022, 42, 2; 349-362
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Sharp Upper Bounds on the Signless Laplacian Spectral Radius of Strongly Connected Digraphs
Autorzy:
Xi, Weige
Wang, Ligong
Powiązania:
https://bibliotekanauki.pl/articles/31340590.pdf
Data publikacji:
2016-11-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
digraph
signless Laplacian spectral radius
Opis:
Let \( G = (V (G),E(G)) \) be a simple strongly connected digraph and \( q(G) \) be the signless Laplacian spectral radius of \( G \). For any vertex \( v_i \in V (G) \), let \( d+i \) denote the outdegree of \( v_i \), \( m_i^+ \) denote the average 2-outdegree of \( v_i \), and \( N_i^+ \) denote the set of out-neighbors of \( v_i \). In this paper, we prove that: (1) \( q(G) = d_1^+ + d_2^+, (d_1^+ \ne d_2^+ ) \) if and only if \( G \) is a star digraph \( \overleftrightarrow{K}_{1,n-1} \), where \( d_1^+ \), \( d_2^+ \) are the maximum and the second maximum outdegree, respectively (\( \overleftrightarrow{K}_{1,n-1} \) is the digraph on \( n \) vertices obtained from a star graph \( K_{1,n−1} \) by replacing each edge with a pair of oppositely directed arcs). (2) \( q(G) \le \text{max} \bigg\{ \frac{1}{2} \left( d_i^+ + \sqrt{ { d_i^+ }^2 + 8d_i^+ m_i^+ } \right) : v_i \in V(G) \bigg\} \) with equality if and only if \( G \) is a regular digraph. (3) \( q(G) \le \text{max} \bigg\{ \frac{1}{2} \left( d_i^+ + \sqrt{ {d_i^+}^2 + \frac{4}{d_i^+} \sum_{v_j \in N_i^+ } d_j^+ ( d_j^+ + m_j^+ ) } \right) : v_i \in V(G) \bigg\} \). Moreover, the equality holds if and only if \( G \) is a regular digraph or a bipartite semiregular digraph. (4) \( q(G) \le \text{max} \big\{ \frac{1}{2} \left( d_i^+ + 2d_j^+ - 1 + \sqrt{ ( d_i^+ - 2d_j^+ + 1 )^2 + 4d_i^+ } \right) : ( v_j, v_i ) \in E(G) \big\} \). If the equality holds, then \( G \) is a regular digraph or \( G \in \Omega \), where \( \Omega \) is a class of digraphs defined in this paper.
Źródło:
Discussiones Mathematicae Graph Theory; 2016, 36, 4; 977-988
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On Implicit Heavy Subgraphs and Hamiltonicity of 2-Connected Graphs
Autorzy:
Zheng, Wei
Wideł, Wojciech
Wang, Ligong
Powiązania:
https://bibliotekanauki.pl/articles/32083821.pdf
Data publikacji:
2021-02-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
implicit degree
implicit o-heavy
implicit f-heavy
implicit c-heavy
Hamilton cycle
Opis:
A graph G of order n is implicit claw-heavy if in every induced copy of K1,3 in G there are two non-adjacent vertices with sum of their implicit degrees at least n. We study various implicit degree conditions (including, but not limiting to, Ore- and Fan-type conditions) imposing of which on specific induced subgraphs of a 2-connected implicit claw-heavy graph ensures its Hamiltonicity. In particular, we improve a recent result of [X. Huang, Implicit degree condition for Hamiltonicity of 2-heavy graphs, Discrete Appl. Math. 219 (2017) 126–131] and complete the characterizations of pairs of o-heavy and f-heavy subgraphs for Hamiltonicity of 2-connected graphs.
Źródło:
Discussiones Mathematicae Graph Theory; 2021, 41, 1; 167-181
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Toughness, Forbidden Subgraphs, and Hamilton-Connected Graphs
Autorzy:
Zheng, Wei
Broersma, Hajo
Wang, Ligong
Powiązania:
https://bibliotekanauki.pl/articles/32361744.pdf
Data publikacji:
2022-02-01
Wydawca:
Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
Tematy:
toughness
forbidden subgraph
Hamilton-connected graph
Hamiltonicity
Opis:
A graph G is called Hamilton-connected if for every pair of distinct vertices {u, v} of G there exists a Hamilton path in G that connects u and v. A graph G is said to be t-tough if t·ω(G − X) ≤ |X| for all X ⊆ V (G) with ω(G − X) > 1. The toughness of G, denoted τ (G), is the maximum value of t such that G is t-tough (taking τ (Kn) = ∞ for all n ≥ 1). It is known that a Hamilton-connected graph G has toughness τ (G) > 1, but that the reverse statement does not hold in general. In this paper, we investigate all possible forbidden subgraphs H such that every H-free graph G with τ (G) > 1 is Hamilton-connected. We find that the results are completely analogous to the Hamiltonian case: every graph H such that any 1-tough H-free graph is Hamiltonian also ensures that every H-free graph with toughness larger than one is Hamilton-connected. And similarly, there is no other forbidden subgraph having this property, except possibly for the graph K1 ∪ P4 itself. We leave this as an open case.
Źródło:
Discussiones Mathematicae Graph Theory; 2022, 42, 1; 187-196
2083-5892
Pojawia się w:
Discussiones Mathematicae Graph Theory
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-5 z 5

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