Degree Conditions for k-Hamiltonian [a, b]-factors

2021 ◽  
Vol 37 (2) ◽  
pp. 232-239
Author(s):  
Jie Wu ◽  
Si-zhong Zhou
Keyword(s):  



1995 ◽  
Vol 19 (3) ◽  
pp. 397-409 ◽  
Author(s):  
Ralph Faudree ◽  
Ronald J. Gould ◽  
Linda Lesniak ◽  
Terri Lindquester


10.37236/3610 ◽  
2015 ◽  
Vol 22 (4) ◽  
Author(s):  
Louis DeBiasio ◽  
Theodore Molla

In 1960 Ghouila-Houri extended Dirac's theorem to directed graphs by proving that if $D$ is a directed graph on $n$ vertices with minimum out-degree and in-degree at least $n/2$, then $D$ contains a directed Hamiltonian cycle. For directed graphs one may ask for other orientations of a Hamiltonian cycle and in 1980 Grant initiated the problem of determining minimum degree conditions for a directed graph $D$ to contain an anti-directed Hamiltonian cycle (an orientation in which consecutive edges alternate direction). We prove that for sufficiently large even $n$, if $D$ is a directed graph on $n$ vertices with minimum out-degree and in-degree at least $\frac{n}{2}+1$, then $D$ contains an anti-directed Hamiltonian cycle. In fact, we prove the stronger result that $\frac{n}{2}$ is sufficient unless $D$ is one of two counterexamples. This result is sharp.



10.37236/7353 ◽  
2019 ◽  
Vol 26 (2) ◽  
Author(s):  
Jinko Kanno ◽  
Songling Shan

Let $G$ be a simple graph, and let $\Delta(G)$ and $\chi'(G)$ denote the maximum degree and chromatic index of $G$, respectively. Vizing proved that $\chi'(G)=\Delta(G)$ or $\chi'(G)=\Delta(G)+1$. We say $G$ is $\Delta$-critical if $\chi'(G)=\Delta(G)+1$ and $\chi'(H)<\chi'(G)$ for every proper subgraph $H$ of $G$. In 1968, Vizing conjectured that if $G$ is a $\Delta$-critical graph, then  $G$ has a 2-factor. Let $G$ be an $n$-vertex $\Delta$-critical graph. It was proved that if $\Delta(G)\ge n/2$, then $G$ has a 2-factor; and that if $\Delta(G)\ge 2n/3+13$, then $G$  has a hamiltonian cycle, and thus a 2-factor. It is well known that every 2-tough graph with at least three vertices has a 2-factor. We investigate the existence of a 2-factor in a $\Delta$-critical graph under "moderate" given toughness and  maximum degree conditions. In particular, we show that  if $G$ is an  $n$-vertex $\Delta$-critical graph with toughness at least 3/2 and with maximum degree at least $n/3$, then $G$ has a 2-factor. We also construct a family of graphs that have order $n$, maximum degree $n-1$, toughness at least $3/2$, but have no 2-factor. This implies that the $\Delta$-criticality in the result is needed. In addition, we develop new techniques in proving the existence of 2-factors in graphs.



2020 ◽  
Vol 34 (4) ◽  
pp. 2108-2123
Author(s):  
Guido Besomi ◽  
Matías Pavez-Signé ◽  
Maya Stein


2011 ◽  
Vol 5 (1) ◽  
pp. 21-25 ◽  
Author(s):  
Roman Čada ◽  
Evelyne Flandrin ◽  
Haiyan Kang
Keyword(s):  


2005 ◽  
Vol 301 (2-3) ◽  
pp. 228-231 ◽  
Author(s):  
Ch. Sobhan Babu ◽  
Ajit A. Diwan
Keyword(s):  


2006 ◽  
Vol 19 (4) ◽  
pp. 491-497
Author(s):  
Jianxiang Li ◽  
Yinghong Ma


2011 ◽  
Vol 311 (18-19) ◽  
pp. 2037-2043 ◽  
Author(s):  
D. Bauer ◽  
M. Yatauro ◽  
N. Kahl ◽  
E. Schmeichel


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