Примеры использования Planar graph can на Английском языке и их переводы на Русский язык
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By the four color theorem, every planar graph can be 4-colored.
Therefore, if every planar graph can be represented in this way with only four directions, then the four color theorem follows.
A remarkable theorem of Kasteleyn states that the number of perfect matchings in a planar graph can be computed exactly in polynomial time via the FKT algorithm.
Conversely, if some planar graph cannot occur as a minor for graphs in family F, then there is a constant k such that all graphs in F have treewidth at most k.
The circle packing theorem states that every planar graph can be represented as a contact graph of circles.
Because the dual graph depends on a particular embedding, the dual graph of a planar graph is not unique, in the sense that the same planar graph can have non-isomorphic dual graphs. .
The result that every simple planar graph can be drawn with straight line edges is called Fáry's theorem.
The construction involves a strengthened form of the separator theorem in which the size of the three subsets of vertices in the separator does not depend on the graph structure: there exists a number c, the magnitude of which at most a constant times√n,such that the vertices of every n-vertex planar graph can be separated into subsets A, S, and B, with no edges from A to B, with|S| c, and with|A||B|(n- c)/2.
One consequence of this theorem is that every planar graph can be decomposed into an independent set and two induced forests.
A corollary of this theorem is that if a planar graph can be embedded in such a way that all but one face has a number of sides that is 2 mod 3, and the remaining face has a number of sides that is not 2 mod 3, then the graph is not Hamiltonian.
That is, every convex polyhedron forms a 3-connected planar graph, and every 3-connected planar graph can be represented as the graph of a convex polyhedron.
By the circle packing theorem, this planar graph can be represented by a circle packing C in which all the edges(including the ones incident to the boundary vertex) are represented by tangencies of circles.
The prototypical example of bend minimization is Fáry's theorem,which states that every planar graph can be drawn with no bends, that is, with all its edges drawn as straight line segments.
They proved that every triangle-free planar graph can be represented by a collection of line segments, with three slopes, such that two vertices of the graph are adjacent if and only if the line segments representing them cross.
The planar separator theorem is a form of isoperimetric inequality for planar graphs, that states that any planar graph can be split into smaller pieces by removing a small number of vertices.
Based on this two-dimensional partial order property, every st-planar graph can be given a dominance drawing, in which for every two vertices u and v there exists a path from u to v if and only if both coordinates of u are smaller than the corresponding coordinates of v. The coordinates of such a drawing may also be used as a data structure that can be used to test whether one vertex of an st-planar graph can reach another in constant time per query.
Every chordal graph can be decomposed in this way into a clique-sum of complete graphs, and every maximal planar graph can be decomposed into a clique-sum of 4-vertex-connected maximal planar graphs.
Tutte's spring theorem states that every 3-connected planar graph can be drawn on a plane without crossings so that its edges are straight line segments and an outside face is a convex polygon Tutte 1963.
Scheinerman's conjecture(now a theorem)states that every planar graph can be represented as an intersection graph of line segments in the plane.
The bound of 4n- 8 on the maximum possible number of edges in a 1-planar graph can be used to show that the complete graph K7 on seven vertices is not 1-planar, because this graph has 21 edges and in this case 4n- 8 20< 21.
Hartman, Newman& Ziv(1991) and de Fraysseix, Ossona de Mendez& Pach(1991)proved that every bipartite planar graph can be represented as an intersection graph of horizontal and vertical line segments; for this result see also Czyzowicz.
Prior to the proof of the four color theorem,he proved that every nearly planar graph can be colored with at most four colors, except for the graphs formed from a wheel graph with an odd outer cycle by replacing the hub vertex with two adjacent vertices, which require five colors.
The four color theorem states that the vertices of every planar graph can be colored with four colors, so that no two adjacent vertices have equal colors.
Steinitz's theorem states that every 3-connected planar graph can be represented as the edges of a convex polyhedron in three-dimensional space.
The case n 5 of Albertson's conjecture is equivalent to the four color theorem, that any planar graph can be colored with four or fewer colors, for the only graphs requiring fewer crossings than the one crossing of K5 are the planar graphs, and the conjecture implies that these should all be at most 4-chromatic.
This conjecture was formulated by E. R. Scheinerman in his Ph.D. thesis(1984),following earlier results that every planar graph could be represented as the intersection graph of a set of simple curves in the plane Ehrlich, Even& Tarjan 1976.
Here, vertices of G are represented by straight line segments and edges of G are represented by intersection points. Scheinerman also conjectured that segments with only three directions would be sufficient to represent 3-colorable graphs, and West(1991)conjectured that analogously every planar graph could be represented using four directions.
Grötzsch's theorem that triangle-free planar graphs can always be colored with at most three colors.
In particular, there exists a planar graph without 4-cycles that cannot be 3-colored.
The planar separator theorem states that a similar partition can be constructed in any planar graph.