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Distance perfectness of graphs

Andrzej Włoch (1999)

Discussiones Mathematicae Graph Theory

In this paper, we propose a generalization of well known kinds of perfectness of graphs in terms of distances between vertices. We introduce generalizations of α-perfect, χ-perfect, strongly perfect graphs and we establish the relations between them. Moreover, we give sufficient conditions for graphs to be perfect in generalized sense. Other generalizations of perfectness are given in papers [3] and [7].

Distance-Locally Disconnected Graphs

Mirka Miller, Joe Ryan, Zdeněk Ryjáček (2013)

Discussiones Mathematicae Graph Theory

For an integer k ≥ 1, we say that a (finite simple undirected) graph G is k-distance-locally disconnected, or simply k-locally disconnected if, for any x ∈ V (G), the set of vertices at distance at least 1 and at most k from x induces in G a disconnected graph. In this paper we study the asymptotic behavior of the number of edges of a k-locally disconnected graph on n vertices. For general graphs, we show that this number is Θ(n2) for any fixed value of k and, in the special case of regular graphs,...

Distances between rooted trees

Bohdan Zelinka (1991)

Mathematica Bohemica

Two types of a distance between isomorphism classes of graphs are adapted for rooted trees.

Distances on the tropical line determined by two points

María Jesús de la Puente (2014)

Kybernetika

Let p ' and q ' be points in n . Write p ' q ' if p ' - q ' is a multiple of ( 1 , ... , 1 ) . Two different points p and q in n / uniquely determine a tropical line L ( p , q ) passing through them and stable under small perturbations. This line is a balanced unrooted semi-labeled tree on n leaves. It is also a metric graph. If some representatives p ' and q ' of p and q are the first and second columns of some real normal idempotent order n matrix A , we prove that the tree L ( p , q ) is described by a matrix F , easily obtained from A . We also prove that...

Distinct equilateral triangle dissections of convex regions

Diane M. Donovan, James G. Lefevre, Thomas A. McCourt, Nicholas J. Cavenagh (2012)

Commentationes Mathematicae Universitatis Carolinae

We define a proper triangulation to be a dissection of an integer sided equilateral triangle into smaller, integer sided equilateral triangles such that no point is the vertex of more than three of the smaller triangles. In this paper we establish necessary and sufficient conditions for a proper triangulation of a convex region to exist. Moreover we establish precisely when at least two such equilateral triangle dissections exist. We also provide necessary and sufficient conditions for some convex...

Distinguishing Cartesian Products of Countable Graphs

Ehsan Estaji, Wilfried Imrich, Rafał Kalinowski, Monika Pilśniak, Thomas Tucker (2017)

Discussiones Mathematicae Graph Theory

The distinguishing number D(G) of a graph G is the minimum number of colors needed to color the vertices of G such that the coloring is preserved only by the trivial automorphism. In this paper we improve results about the distinguishing number of Cartesian products of finite and infinite graphs by removing restrictions to prime or relatively prime factors.

Distinguishing graphs by the number of homomorphisms

Steve Fisk (1995)

Discussiones Mathematicae Graph Theory

A homomorphism from one graph to another is a map that sends vertices to vertices and edges to edges. We denote the number of homomorphisms from G to H by |G → H|. If 𝓕 is a collection of graphs, we say that 𝓕 distinguishes graphs G and H if there is some member X of 𝓕 such that |G → X | ≠ |H → X|. 𝓕 is a distinguishing family if it distinguishes all pairs of graphs. We show that various collections of graphs are a distinguishing family.

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