Примери коришћења Perfect graphs на Енглеском и њихови преводи на Српски
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Algorithms on perfect graphs.
In his initial work on perfect graphs, Berge made two important conjectures on their structure that were only proved later.
König's theorem and perfect graphs.
The perfect graphs are those for which this lower bound is tight, not just in the graph itself but in all of its induced subgraphs.
Some of the more well-known perfect graphs are.
The perfect graphs include many important families of graphs, and serve to unify results relating colorings and cliques in those families.
For many years the complexity of recognizing Berge graphs and perfect graphs remained open.
For instance, in all perfect graphs, the graph coloring problem, maximum clique problem, and maximum independent set problem can all be solved in polynomial time.
The second theorem, conjectured by Berge,provided a forbidden graph characterization of the perfect graphs. An induced cycle of odd length at least 5 is called an odd hole.
Some of the more well-known perfect graphs are: Bipartite graphs, the graphs that can be colored with two colors, including the forests, graphs with no cycles.
The bipartite graphs, line graphs of bipartite graphs, andtheir complements form four out of the five basic classes of perfect graphs used in the proof of the strong perfect graph theorem.[20].
In all perfect graphs, the graph coloring problem, maximum clique problem, and maximum independent set problem can all be solved in polynomial time(Grötschel, Lovász& Schrijver 1988).
All these problems are NP-complete in general, but for example for perfect graphs, it is shown that they can be solved in polynomial time by making use of the ellipsoid method.
In graph theory, a perfect graph is a graph in which the chromatic number of every induced subgraph equals the size of the largest clique of that subgraph.Due to the strong perfect graph theorem, perfect graphs are the same as Berge graphs. .
These include the interval graphs, trivially perfect graphs, threshold graphs, windmill graphs, and permutation graphs; their complements are a subset of the comparability graphs. .
The theory of perfect graphs developed from a 1958 result of Tibor Gallai that in modern language can be interpreted as stating that the complement of a bipartite graph is perfect; this result can also be viewed as a simple equivalent of König's theorem, a much earlier result relating matchings and vertex covers in bipartite graphs. .
The first use of the phrase"perfect graph" appears to be in a 1963paper of Claude Berge, after whom Berge graphs are named. 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.
Another class of related results concerns perfect graphs: every bipartite graph, the complement of every bipartite graph, the line graph of every bipartite graph, and the complement of the line graph of every bipartite graph, are all perfect. .
Comparability graphs formed from partially ordered sets by connecting pairs of elements by an edge whenever they are related in the partial order. These include the bipartite graphs, the complements of interval graphs, the trivially perfect graphs, the threshold graphs, the windmill graphs, the permutation graphs(graphs in which the edges represent pairs of elements that are reversed by a permutation), and the cographs(graphs formed by recursive operations of disjoint union and complementation).
According to the strong perfect graph theorem, the perfect graphs have a forbidden graph characterization resembling that of bipartite graphs: a graph is bipartite if and only if it has no odd cycle as a subgraph, and a graph is perfect if and only if it has no odd cycle or its complement as an induced subgraph.
It is of great interest to see whether the same optimization problems can be solved for perfect graphs by polynomial time purely combinatorial algorithms. The planned investigations are natural extension of successful research and international cooperation in the past.
This was one of the results that motivated the initial definition of perfect graphs.[19] Perfection of the complements of line graphs of perfect graphs is yet another restatement of König's theorem, and perfection of the line graphs themselves is a restatement of an earlier theorem of König, that every bipartite graph has an edge coloring using a number of colors equal to its maximum degree.
The first of these two theorems was the perfect graph theorem of Lovász(1972), stating that a graph is perfect if and only if its complement is perfect. .
Because these graphs are not perfect, every perfect graph must be a Berge graph, a graph with no odd holes and no odd antiholes.
The perfect graph theorem has a short proof, but the proof of the strong perfect graph theorem is long and technical, based on a deep structural decomposition of Berge graphs. .
(Alternatively, the imperfection of this graph follows from the perfect graph theorem and the imperfection of the complementary odd cycle).
Characterizations and the perfect graph theorems.
This was finally proven as the strong perfect graph theorem of Chudnovsky, Robertson, Seymour, and Thomas(2006).
Finally, subsequent to the proof of the strong perfect graph theorem, a polynomial time algorithm was discovered by Chudnovsky, Cornuéjols, Liu, Seymour, and Vušković.
The conjecture remained unresolved for 40 years,until it was established as the celebrated strong perfect graph theorem by Chudnovsky, Robertson, Seymour, and Thomas in 2002.