Alspach's Problem: The Case of Hamilton Cycles and 5-Cycles

Heather Jordon

doi:10.37236/569

Alspach's Problem: The Case of Hamilton Cycles and 5-Cycles

The Electronic Journal of Combinatorics ◽

10.37236/569 ◽

2011 ◽

Vol 18 (1) ◽

Author(s):

Heather Jordon

Keyword(s):

Complete Graph ◽

Hamilton Cycles

In this paper, we settle Alspach's problem in the case of Hamilton cycles and 5-cycles; that is, we show that for all odd integers $n\ge 5$ and all nonnegative integers $h$ and $t$ with $hn + 5t = n(n-1)/2$, the complete graph $K_n$ decomposes into $h$ Hamilton cycles and $t$ 5-cycles and for all even integers $n \ge 6$ and all nonnegative integers $h$ and $t$ with $hn + 5t = n(n-2)/2$, the complete graph $K_n$ decomposes into $h$ Hamilton cycles, $t$ 5-cycles, and a $1$-factor. We also settle Alspach's problem in the case of Hamilton cycles and 4-cycles.

Download Full-text

Multicoloured Hamilton Cycles

The Electronic Journal of Combinatorics ◽

10.37236/1204 ◽

1995 ◽

Vol 2 (1) ◽

Cited By ~ 35

Author(s):

Michael Albert ◽

Alan Frieze ◽

Bruce Reed

Keyword(s):

Complete Graph ◽

Hamiltonian Cycle ◽

Proof Technique ◽

Hamilton Cycles ◽

Local Lemma

The edges of the complete graph $K_n$ are coloured so that no colour appears more than $\lceil cn\rceil$ times, where $c < 1/32$ is a constant. We show that if $n$ is sufficiently large then there is a Hamiltonian cycle in which each edge is a different colour, thereby proving a 1986 conjecture of Hahn and Thomassen. We prove a similar result for the complete digraph with $c < 1/64$. We also show, by essentially the same technique, that if $t\geq 3$, $c < (2t^2(1+t))^{-1}$, no colour appears more than $\lceil cn\rceil$ times and $t|n$ then the vertices can be partitioned into $n/t$ $t-$sets $K_1,K_2,\ldots,K_{n/t}$ such that the colours of the $n(t-1)/2$ edges contained in the $K_i$'s are distinct. The proof technique follows the lines of Erdős and Spencer's modification of the Local Lemma.

Download Full-text

Fast Strategies in Waiter-Client Games

The Electronic Journal of Combinatorics ◽

10.37236/9451 ◽

2020 ◽

Vol 27 (3) ◽

Author(s):

Dennis Clemens ◽

Pranshu Gupta ◽

Fabian Hamann ◽

Alexander Haupt ◽

Mirjana Mikalački ◽

...

Keyword(s):

Complete Graph ◽

Spanning Trees ◽

Perfect Matchings ◽

Hamilton Cycles ◽

The Family ◽

Winning Set ◽

Pancyclic Graphs

Waiter-Client games are played on some hypergraph $(X,\mathcal{F})$, where $\mathcal{F}$ denotes the family of winning sets. For some bias $b$, during each round of such a game Waiter offers to Client $b+1$ elements of $X$, of which Client claims one for himself while the rest go to Waiter. Proceeding like this Waiter wins the game if she forces Client to claim all the elements of any winning set from $\mathcal{F}$. In this paper we study fast strategies for several Waiter-Client games played on the edge set of the complete graph, i.e. $X=E(K_n)$, in which the winning sets are perfect matchings, Hamilton cycles, pancyclic graphs, fixed spanning trees or factors of a given graph.

Download Full-text

On the Generalized Distance Energy of Graphs

Mathematics ◽

10.3390/math8010017 ◽

2019 ◽

Vol 8 (1) ◽

pp. 17 ◽

Cited By ~ 4

Author(s):

Abdollah Alhevaz ◽

Maryam Baghipur ◽

Hilal A. Ganie ◽

Yilun Shang

Keyword(s):

Lower Bounds ◽

Complete Graph ◽

Connected Graph ◽

Distance Matrix ◽

Wiener Index ◽

Diagonal Matrix ◽

Upper And Lower Bounds ◽

Star Graph ◽

Extremal Graphs ◽

Generalized Distance

The generalized distance matrix D α ( G ) of a connected graph G is defined as D α ( G ) = α T r ( G ) + ( 1 − α ) D ( G ) , where 0 ≤ α ≤ 1 , D ( G ) is the distance matrix and T r ( G ) is the diagonal matrix of the node transmissions. In this paper, we extend the concept of energy to the generalized distance matrix and define the generalized distance energy E D α ( G ) . Some new upper and lower bounds for the generalized distance energy E D α ( G ) of G are established based on parameters including the Wiener index W ( G ) and the transmission degrees. Extremal graphs attaining these bounds are identified. It is found that the complete graph has the minimum generalized distance energy among all connected graphs, while the minimum is attained by the star graph among trees of order n.

Download Full-text

On the Second-Largest Reciprocal Distance Signless Laplacian Eigenvalue

Mathematics ◽

10.3390/math9050512 ◽

2021 ◽

Vol 9 (5) ◽

pp. 512

Author(s):

Maryam Baghipur ◽

Modjtaba Ghorbani ◽

Hilal A. Ganie ◽

Yilun Shang

Keyword(s):

Lower Bounds ◽

Complete Graph ◽

Distance Matrix ◽

Upper And Lower Bounds ◽

Laplacian Eigenvalue ◽

Signless Laplacian ◽

Graph Parameters ◽

Simple Connected Graph ◽

Second Largest Eigenvalue ◽

Reciprocal Distance Matrix

The signless Laplacian reciprocal distance matrix for a simple connected graph G is defined as RQ(G)=diag(RH(G))+RD(G). Here, RD(G) is the Harary matrix (also called reciprocal distance matrix) while diag(RH(G)) represents the diagonal matrix of the total reciprocal distance vertices. In the present work, some upper and lower bounds for the second-largest eigenvalue of the signless Laplacian reciprocal distance matrix of graphs in terms of various graph parameters are investigated. Besides, all graphs attaining these new bounds are characterized. Additionally, it is inferred that among all connected graphs with n vertices, the complete graph Kn and the graph Kn−e obtained from Kn by deleting an edge e have the maximum second-largest signless Laplacian reciprocal distance eigenvalue.

Download Full-text

Undirected Complete Graph to Design New Public Key Cryptosystem

Journal of Physics Conference Series ◽

10.1088/1742-6596/1897/1/012045 ◽

2021 ◽

Vol 1897 (1) ◽

pp. 012045

Author(s):

Karrar Taher R. Aljamaly ◽

Ruma Kareem K. Ajeena

Keyword(s):

Complete Graph ◽

Public Key ◽

Public Key Cryptosystem ◽

New Public

Download Full-text

Turán theorems for unavoidable patterns

Mathematical Proceedings of the Cambridge Philosophical Society ◽

10.1017/s030500412100027x ◽

2021 ◽

pp. 1-20

Author(s):

ANTÓNIO GIRÃO ◽

BHARGAV NARAYANAN

Keyword(s):

Complete Graph ◽

Blow Up ◽

Ramsey Numbers ◽

Order Of Magnitude ◽

Transitive Tournament ◽

Unavoidable Patterns

Abstract We prove Turán-type theorems for two related Ramsey problems raised by Bollobás and by Fox and Sudakov. First, for t ≥ 3, we show that any two-colouring of the complete graph on n vertices that is δ-far from being monochromatic contains an unavoidable t-colouring when δ ≫ n−1/t, where an unavoidable t-colouring is any two-colouring of a clique of order 2t in which one colour forms either a clique of order t or two disjoint cliques of order t. Next, for t ≥ 3, we show that any tournament on n vertices that is δ-far from being transitive contains an unavoidable t-tournament when δ ≫ n−1/[t/2], where an unavoidable t-tournament is the blow-up of a cyclic triangle obtained by replacing each vertex of the triangle by a transitive tournament of order t. Conditional on a well-known conjecture about bipartite Turán numbers, both our results are sharp up to implied constants and hence determine the order of magnitude of the corresponding off-diagonal Ramsey numbers.

Download Full-text

Counting Hamilton cycles in Dirac hypergraphs

Combinatorics Probability Computing ◽

10.1017/s0963548320000619 ◽

2020 ◽

pp. 1-23

Author(s):

Stefan Glock ◽

Stephen Gould ◽

Felix Joos ◽

Daniela Kühn ◽

Deryk Osthus

Keyword(s):

Hamilton Cycle ◽

Uniform Hypergraph ◽

Similar Estimate ◽

Hamilton Cycles

Abstract A tight Hamilton cycle in a k-uniform hypergraph (k-graph) G is a cyclic ordering of the vertices of G such that every set of k consecutive vertices in the ordering forms an edge. Rödl, Ruciński and Szemerédi proved that for $k\ge 3$ , every k-graph on n vertices with minimum codegree at least $n/2+o(n)$ contains a tight Hamilton cycle. We show that the number of tight Hamilton cycles in such k-graphs is ${\exp(n\ln n-\Theta(n))}$ . As a corollary, we obtain a similar estimate on the number of Hamilton ${\ell}$ -cycles in such k-graphs for all ${\ell\in\{0,\ldots,k-1\}}$ , which makes progress on a question of Ferber, Krivelevich and Sudakov.

Download Full-text