Search results
Results From The WOW.Com Content Network
Given a function: from a set X (the domain) to a set Y (the codomain), the graph of the function is the set [4] = {(, ()):}, which is a subset of the Cartesian product.In the definition of a function in terms of set theory, it is common to identify a function with its graph, although, formally, a function is formed by the triple consisting of its domain, its codomain and its graph.
The permutation graph of the permutation (4,3,5,1,2) connects pairs of elements whose ordering is reversed by the permutation. A permutation graph is defined from a permutation on a totally ordered sequence of elements (conventionally, the integers from to ), which form the vertices of the graph. The edges of a permutation graph connect pairs ...
In graph theory, the perfect graph theorem of László Lovász (1972a, 1972b) states that an undirected graph is perfect if and only if its complement graph is also perfect. This result had been conjectured by Berge ( 1961 , 1963 ), and it is sometimes called the weak perfect graph theorem to distinguish it from the strong perfect graph theorem ...
The source merge S = M(X,Y) of two TTGs X and Y is a TTG created from the disjoint union of graphs X and Y by merging the source of X with the source of Y. The source and sink of X become the source and sink of S respectively. An SPQR tree is a tree structure that can be defined for an arbitrary 2-vertex-connected graph. It has S-nodes, which ...
where a = 5(4ν + 3) / ν 2 + 1 . Using the negative case of the square root yields, after scaling variables, the first parametrization while the positive case gives the second. The substitution c = −m / ℓ 5 , e = 1 / ℓ in the Spearman–Williams parameterization allows one to not exclude the special case a = 0 ...
Proof without words that a hypercube graph is non-planar using Kuratowski's or Wagner's theorems and finding either K 5 (top) or K 3,3 (bottom) subgraphs. If is a graph that contains a subgraph that is a subdivision of or ,, then is known as a Kuratowski subgraph of . [1]
The points P 1, P 2, and P 3 (in blue) are collinear and belong to the graph of x 3 + 3 / 2 x 2 − 5 / 2 x + 5 / 4 . The points T 1, T 2, and T 3 (in red) are the intersections of the (dotted) tangent lines to the graph at these points with the graph itself. They are collinear too.
The case = is also easy: the graphs requiring three colors are the non-bipartite graphs, and every non-bipartite graph has an odd cycle, which can be contracted to a 3-cycle, that is, a minor. In the same paper in which he introduced the conjecture, Hadwiger proved its truth for =.