18 research outputs found
The Cycle Spectrum of Claw-free Hamiltonian Graphs
If is a claw-free hamiltonian graph of order and maximum degree
with , then has cycles of at least many different lengths.Comment: 9 page
Hamiltonicity, independence number, and pancyclicity
A graph on n vertices is called pancyclic if it contains a cycle of length l
for all 3 \le l \le n. In 1972, Erdos proved that if G is a Hamiltonian graph
on n > 4k^4 vertices with independence number k, then G is pancyclic. He then
suggested that n = \Omega(k^2) should already be enough to guarantee
pancyclicity. Improving on his and some other later results, we prove that
there exists a constant c such that n > ck^{7/3} suffices
Pancyclicity of Hamiltonian line graphs
Let f(n) be the smallest integer such that for every graph G of order n with minimum degree 3(G)>f(n), the line graph L(G) of G is pancyclic whenever L(G) is hamiltonian. Results are proved showing that f(n) = ®(n 1/3)
Hamiltonicity, Pancyclicity, and Cycle Extendability in Graphs
The study of cycles, particularly Hamiltonian cycles, is very important in many applications.
Bondy posited his famous metaconjecture, that every condition sufficient for Hamiltonicity actually guarantees a graph is pancyclic. Pancyclicity is a stronger structural property than Hamiltonicity.
An even stronger structural property is for a graph to be cycle extendable. Hendry conjectured that any graph which is Hamiltonian and chordal is cycle extendable.
In this dissertation, cycle extendability is investigated and generalized. It is proved that chordal 2-connected K1,3-free graphs are cycle extendable. S-cycle extendability was defined by Beasley and Brown, where S is any set of positive integers. A conjecture is presented that Hamiltonian chordal graphs are {1, 2}-cycle extendable.
Dirac’s Theorem is an classic result establishing a minimum degree condition for a graph to be Hamiltonian. Ore’s condition is another early result giving a sufficient condition for Hamiltonicity. In this dissertation, generalizations of Dirac’s and Ore’s Theorems are presented.
The Chvatal-Erdos condition is a result showing that if the maximum size of an independent set in a graph G is less than or equal to the minimum number of vertices whose deletion increases the number of components of G, then G is Hamiltonian. It is proved here that the Chvatal-Erdos condition guarantees that a graph is cycle extendable. It is also shown that a graph having a Hamiltonian elimination ordering is cycle extendable.
The existence of Hamiltonian cycles which avoid sets of edges of a certain size and certain subgraphs is a new topic recently investigated by Harlan, et al., which clearly has applications to scheduling and communication networks among other things. The theory is extended here to bipartite graphs. Specifically, the conditions for the existence of a Hamiltonian cycle that avoids edges, or some subgraph of a certain size, are determined for the bipartite case.
Briefly, this dissertation contributes to the state of the art of Hamiltonian cycles, cycle extendability and edge and graph avoiding Hamiltonian cycles, which is an important area of graph theory
A Survey of Best Monotone Degree Conditions for Graph Properties
We survey sufficient degree conditions, for a variety of graph properties,
that are best possible in the same sense that Chvatal's well-known degree
condition for hamiltonicity is best possible.Comment: 25 page
Pancyclicity of Hamiltonian and highly connected graphs
A graph G on n vertices is Hamiltonian if it contains a cycle of length n and
pancyclic if it contains cycles of length for all .
Write for the independence number of , i.e. the size of the
largest subset of the vertex set that does not contain an edge, and
for the (vertex) connectivity, i.e. the size of the smallest subset of the
vertex set that can be deleted to obtain a disconnected graph. A celebrated
theorem of Chv\'atal and Erd\H{o}s says that is Hamiltonian if . Moreover, Bondy suggested that almost any non-trivial
conditions for Hamiltonicity of a graph should also imply pancyclicity.
Motivated by this, we prove that if then G is
pancyclic. This establishes a conjecture of Jackson and Ordaz up to a constant
factor. Moreover, we obtain the more general result that if G is Hamiltonian
with minimum degree then G is pancyclic. Improving
an old result of Erd\H{o}s, we also show that G is pancyclic if it is
Hamiltonian and . Our arguments use the following theorem
of independent interest on cycle lengths in graphs: if then G contains a cycle of length for all .Comment: 15 pages, 1 figur
Best monotone degree conditions for binding number
AbstractWe give sufficient conditions on the vertex degrees of a graph G to guarantee that G has binding number at least b, for any given b>0. Our conditions are best possible in exactly the same way that Chvátal’s well-known degree condition to guarantee a graph is Hamiltonian is best possible