Примеры использования Chromatic polynomial на Английском языке и их переводы на Русский язык
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Today, chromatic polynomials are one of the central objects of algebraic graph theory.
A graph is chromatically unique if it is determined by its chromatic polynomial, up to isomorphism.
The chromatic polynomial of a graph, for example, counts the number of its proper vertex colorings.
The absolute values of coefficients of every chromatic polynomial form a log-concave sequence.
The chromatic polynomial is categorified by a homology theory closely related to Khovanov homology.
Chao and Novacky(1982) show that the Turángraphs are chromatically unique: no other graphs have the same chromatic polynomials.
Foster had already observed that the chromatic polynomial is one such function, and Tutte began to discover more.
Its chromatic polynomial can be deduced from the chromatic polynomial of the cycle graph C3 and is equal to( x- 2) n( x- 1) n x{\displaystyle( x-2)^{ n}( x-1)^{ n} x.
Acyclic orientations are also related to colorings through the chromatic polynomial, which counts both acyclic orientations and colorings.
In this context the chromatic polynomial counts the number of lattice points in the{\displaystyle}-cube that avoid the graphic arrangement.
Edge contraction is used in the recursive formula for the number of spanning trees of an arbitrary connected graph, andin the recurrence formula for the chromatic polynomial of a simple graph.
Isomorphic graphs have the same chromatic polynomial, but non-isomorphic graphs can be chromatically equivalent.
The problem of computing the number of 3-colorings of a given graph is a canonical example of a P-complete problem,so the problem of computing the coefficients of the chromatic polynomial is P-hard.
A root(or zero) of a chromatic polynomial, called a“chromatic root”, is a value x where P( G, x) 0{\displaystyle P(G, x)=0.
However, there are still many open problems, such as characterizing graphs which have the same chromatic polynomial, and determining which polynomials are chromatic. .
The chromatic polynomial includes at least as much information about the colorability of G as does the chromatic number.
Finally, the third branch of algebraic graph theory concerns algebraic properties of invariants of graphs,and especially the chromatic polynomial, the Tutte polynomial and knot invariants.
George David Birkhoff introduced the chromatic polynomial in 1912, defining it only for planar graphs, in an attempt to prove the four color theorem.
Tutte called this function the dichromate,as he saw it as a generalization of the chromatic polynomial to two variables, but it is usually referred to as the Tutte polynomial. .
Like the chromatic polynomial, the Tutte polynomial T G{\displaystyle T_{G}} of a graph G{\displaystyle G}, can be used to count the number of acyclic orientations of G{\displaystyle G} as T G( 2, 0){\displaystyle T_{G}2,0.
Tutte writes,“Playing with my W-functions I obtained a two-variable polynomial from which either the chromatic polynomial or the flow-polynomial could be obtained by setting one of the variables equal to zero, and adjusting signs.”.
Its chromatic polynomial can be deduced form the chromatic polynomial of the complete graph and is equal to∏ i 0 k- 1( x- i) n.{\displaystyle\prod_{ i=0}^{ k-1}( x-i)^{ n}.} The windmill graph Wd(k, n) is proved not graceful if k> 5.
The number of acyclic orientations may be counted using the chromatic polynomial χ G{\displaystyle\chi_{G}}, whose value at a positive integer k is the number of k-colorings of the graph.
Computational problems associated with the chromatic polynomial include finding the chromatic polynomial P( G, x){\displaystyle P(G, x)} of a given graph G; evaluating P( G, x){\displaystyle P(G, x)} at a fixed point x for given G. The first problem is more general because if we knew the coefficients of P( G, x){\displaystyle P(G, x)} we could evaluate it at any point in polynomial time because the degree is n.
In 1968, Read asked which polynomials are the chromatic polynomials of some graph, a question that remains open, and introduced the concept of chromatically equivalent graphs.
In 1912, George David Birkhoff introduced the chromatic polynomial to study the coloring problems, which was generalised to the Tutte polynomial by Tutte, important structures in algebraic graph theory.
When Birkhoff andLewis introduced the chromatic polynomial in their attack on the four-color theorem, they conjectured that for planar graphs G, the polynomial P( G, t){\displaystyle P(G, t)} has no zeros in the region.
Indeed, χ is the smallest positive integer that is not a root of the chromatic polynomial χ( G) min{ k: P( G, k)> 0}.{\displaystyle\chi( G)=\ min\{ k\,\colon\, P(G, k)>0\}.} An edge coloring of a graph is a proper coloring of the edges, meaning an assignment of colors to edges so that no vertex is incident to two edges of the same color.
Approximating Chromatic Sum Coloring of Bipartite Graphs in Expected Polynomial Time.