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The median of three vertices in a tree, showing the subtree formed by the union of shortest paths between the vertices. Every tree is a median graph. To see this, observe that in a tree, the union of the three shortest paths between pairs of the three vertices a, b, and c is either itself a path, or a subtree formed by three paths meeting at a single central node with degree three.
The squaregraphs include as special cases trees, grid graphs, gear graphs, and the graphs of polyominos.. As well as being planar graphs, squaregraphs are median graphs, meaning that for every three vertices u, v, and w there is a unique median vertex m(u,v,w) that lies on shortest paths between each pair of the three vertices. [1]
The trees and hypercube graphs are examples of median graphs. Since the median graphs include the squaregraphs, simplex graphs, and Fibonacci cubes, as well as the covering graphs of finite distributive lattices, these are all partial cubes. The planar dual graph of an arrangement of lines in the Euclidean plane is a partial cube.
A median graph is an undirected graph in which for every three vertices , , and there is a unique vertex ,, that belongs to shortest paths between any two of , , and . If this is the case, then the operation x , y , z {\displaystyle \langle x,y,z\rangle } defines a median algebra having the vertices of the graph as its elements.
Finite median algebras and median graphs have a dual structure as the set of solutions of a 2-satisfiability instance; Barthélemy & Constantin (1993) formulate this structure equivalently as the family of initial stable sets in a mixed graph. [5] For a distributive lattice, the corresponding mixed graph has no undirected edges, and the initial ...
In the mathematical discipline of graph theory, the medial graph of plane graph G is another graph M(G) that represents the adjacencies between edges in the faces of G. Medial graphs were introduced in 1922 by Ernst Steinitz to study combinatorial properties of convex polyhedra , [ 1 ] although the inverse construction was already used by Peter ...
Reinhard Diestel (born 1959) [1] is a German mathematician specializing in graph theory, including the interplay among graph minors, matroid theory, tree decomposition, and infinite graphs. He holds the chair of discrete mathematics at the University of Hamburg .
Median (geometry), in geometry, a line joining a vertex of a triangle to the midpoint of the opposite side; Median (graph theory), a vertex m(a,b,c) that belongs to shortest paths between each pair of a, b, and c; Median algebra, an algebraic triple product generalising the algebraic properties of the majority function