Примеры использования Perfect graphs на Английском языке и их переводы на Русский язык
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Chordal graphs are a subclass of the well known perfect graphs.
In his initial work on perfect graphs, Berge made two important conjectures on their structure that were only proved later.
For many years the complexity of recognizing Berge graphs and perfect graphs remained open.
The perfect graphs include many important families of graphs, and serve to unify results relating colorings and cliques in those families.
Chu(2008) describes a simple linear time algorithm for recognizing trivially perfect graphs, based on lexicographic breadth-first search.
A chapter on split graphs appears in the book by Martin Charles Golumbic,"Algorithmic Graph Theory and Perfect Graphs.
Because these three types of biconnected component are all perfect graphs themselves, every line perfect graph is itself perfect. .
Perfect graphs include many important graphs classes including bipartite graphs, chordal graphs, and comparability graphs. .
The interval graphs that have an interval representation in which every two intervals are either disjoint ornested are the trivially perfect graphs.
For the perfect graphs, a number of NP-complete optimization problems(graph coloring problem, maximum clique problem, and maximum independent set problem) are polynomially solvable.
The threshold graphs are exactly the graphs that are both themselves trivially perfect andthe complements of trivially perfect graphs co-trivially perfect graphs.
The C 5{\displaystyle C_{5}}-free graphs include the perfect graphs, which necessarily have either a clique or independent set of size proportional to the square root of their number of vertices.
The graph of the figure can be represented as ϵ u u u j u u j{\displaystyle\epsilon uuujuuj} Threshold graphs are a special case of cographs,split graphs, and trivially perfect graphs.
Line perfect graphs generalize the bipartite graphs, and share with them the properties that the maximum matching and minimum vertex cover have the same size, and that the chromatic index equals the maximum degree.
This result had been conjectured by Berge(1961, 1963), andit is sometimes called the weak perfect graph theorem to distinguish it from the strong perfect graph theorem characterizing perfect graphs by their forbidden induced subgraphs.
Perfect graphs may also be described as the graphs in which, in every induced subgraph, the size of the largest independent set is equal to the number of cliques in a partition of the graph's vertices into a minimum number of cliques.
It follows from the equivalent characterizations of trivially perfect graphs that every trivially perfect graph is also a cograph, a chordal graph, a Ptolemaic graph, an interval graph, and a perfect graph. .
Nevertheless, many algorithms for computing cliques have been developed, either running in exponential time(such as the Bron-Kerbosch algorithm) orspecialized to graph families such as planar graphs or perfect graphs for which the problem can be solved in polynomial time.
In this paper he unified Gallai's result with several similar results by defining perfect graphs, and he conjectured the equivalence of the perfect graph and Berge graph definitions; Berge's conjecture was proved in 2002 as the strong perfect graph theorem.
Chudnovsky& Seymour(2005) overview a series of papers in which they prove a structure theory for claw-free graphs, analogous to the graph structure theorem for minor-closed graph families proven by Robertson and Seymour, andto the structure theory for perfect graphs that Chudnovsky, Seymour and their co-authors used to prove the strong perfect graph theorem.
Chordless cycles may be used to characterize perfect graphs: by the strong perfect graph theorem, a graph is perfect if and only if none of its holes or antiholes have an odd number of vertices that is greater than three.
They are the graphs that can be formed, starting from one-vertex graphs, by two operations: disjoint union of two smaller trivially perfect graphs, and the addition of a new vertex adjacent to all the vertices of a smaller trivially perfect graph. .
He observed that perfect graphs cannot contain odd antiholes, induced subgraphs complementary to odd holes: an odd antihole with 2k+ 1 vertices has clique number k and chromatic number k+ 1,again impossible for a perfect graphs.
Line graphs of bipartite graphs form an important family of perfect graphs: they are one of a small number of families used by Chudnovsky et al.(2006) to characterize the perfect graphs and to show that every graph with no odd hole and no odd antihole is perfect. .
In 1960, Claude Berge formulated another conjecture about graph coloring, the strong perfect graph conjecture, originally motivated by an information-theoretic concept called the zero-error capacity of a graph introduced by Shannon.
Subsequent to the proof of the strong perfect graph conjecture, Chudnovsky(2006) simplified it by showing that homogeneous pairs could be eliminated from the set of decompositions used in the proof.
The perfect graph theorem is the special case of this result when one of the three subgraphs is the empty graph. .
Thus, the perfect graph theorem can be used to prove Dilworth's theorem from the(much easier) proof of Mirsky's theorem, or vice versa.
A perfect graph is a graph in which the chromatic number and the size of the maximum clique are equal, and in which this equality persists in every induced subgraph.
Equivalently, in a perfect graph, the size of the maximum independent set equals the minimum number of cliques in a clique cover.