Examples of using Odd cycle in English and their translations into Russian
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Odd cycles are harmonious, as is the Petersen graph.
Correspondingly, the chromatic number of an odd cycle is three.
Removing this edge from the odd cycle leaves a path, which may be colored using the two colors for its subgraph.
Alternatively, the imperfection of this graph follows from the perfect graph theorem andthe imperfection of the complementary odd cycle.
However, if there exists at least one odd cycle, then no 2-edge-coloring is possible.
An odd cycle of length greater than 3 cannot be perfect, because its chromatic number is three and its clique number is two.
For example, all complete graphs Kn and all odd cycles(cycle graphs of odd length) are cores.
As there are no odd cycles in G in that case, blossoms will never be found and one can simply remove lines B20- B24 of the algorithm.
By Brooks' theorem, every k-regular graph(except for odd cycles and cliques) has chromatic number at most k.
See Lovász(1992) If G is(k- 1)-regular, meaning every vertex is adjacent to exactly k- 1 others,then G is either Kk or an odd cycle.
Removing the vertices of an odd cycle transversal from a graph leaves a bipartite graph as the remaining induced subgraph.
This applies only to connected graphs;disconnected counterexamples include disjoint unions of odd cycles, or of copies of K2k+1.
Since the product of two odd cycle graphs contains an odd cycle, the product G× H is not 2-colorable either.
In other words, the list chromatic number of a connected undirected graph G never exceeds Δ,unless G is a clique or an odd cycle.
Similarly, the complement of an odd cycle of length 2k+ 1 cannot be perfect, because its chromatic number is k+ 1 and its clique number is k.
One of these subclasses was the family of claw-free graphs:it was discovered by several authors that claw-free graphs without odd cycles and odd holes are perfect.
After this step, each remaining odd cycle contains at least one edge that may be colored with one of the two colors belonging to the opposite subgraph.
Therefore, if a minimally imperfect graph has a 2-join, it must equal one of its blocks,from which it follows that it must be an odd cycle and not Berge.
For k 3, every k-critical graph(that is, every odd cycle) can be generated as a k-constructible graph such that all of the graphs formed in its construction are also k-critical.
For any connected undirected graph G with maximum degree Δ,the chromatic number of G is at most Δ unless G is a complete graph or an odd cycle, in which case the chromatic number is Δ+ 1.
The problem of finding the smallest odd cycle transversal, or equivalently the largest bipartite induced subgraph, is also called odd cycle transversal, and abbreviated as OCT.
In the other direction, a vertex cover of G◻ K 2{\displaystyle G\square K_{2}}can be transformed into an odd cycle transversal by keeping only the vertices for which both copies are in the cover.
For degree two, any odd cycle is such a graph, and for degree three, four, and five, these graphs can be constructed from platonic solids by replacing a single edge by a path of two adjacent edges.
More specifically, if the thrackle conjecture is true, the thrackles may be exactly characterized by a result of Woodall:they are the pseudoforests in which there is no cycle of length four and at most one odd cycle.
Conversely from a sequence of odd cycle contractions, each containing the vertex formed from the previous contraction, one may form an ear decomposition in which the ears are the sets of edges contracted in each step.
It is now known(the strong perfect graph theorem)that perfect graphs may be characterized as the graphs that do not have as induced subgraphs either an odd cycle or the complement of an odd cycle a so-called odd hole.
The technique was invented by Reed, Smith andVetta to show that the problem of odd cycle transversal was solvable in time O(3k kmn), for a graph with n vertices, m edges, and odd cycle traversal number k.
The odd cycle transversal can be transformed into a vertex cover by including both copies of each vertex from the transversal and one copy of each remaining vertex, selected from the two copies according to which side of the bipartition contains it.
Iterative compression has been used successfully in many problems,for instance odd cycle transversal(see below) and edge bipartization, feedback vertex set, cluster vertex deletion and directed feedback vertex set.
For instance, if one contracts the ears of an ear decomposition, in the order given by the decomposition,then at the time each ear is contracted it forms an odd cycle, so the ear decomposition characterization may be used to find a sequence of odd cycles to contract.