J. Richard Lundgren

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Vertices x and y dominate a tournament T if for all vertices z 6 = x; y; either x beats z or y beats z. Let dom(T) be the graph on the vertices of T with edges between pairs of vertices that dominate T. We show dom(T) is either an odd cycle with possible pendant vertices or a forest of caterpillars. Since dom(T) is the complement of the competition graph of(More)
The pattern of a matrix M is a (0, 1)-matrix which replaces all non-zero entries of M with a 1. A directed graph is said to support M if its adjacency matrix is the pattern of M . If M is an orthogonal matrix, then a digraph which supports M must satisfy a condition known as quadrangularity. We look at quadrangularity in tournaments and determine for which(More)
In the present study we compared the clinical presentations of patients with a clinical diagnosis of AIDS and disseminated Mycobacterium genavense infection (n = 12) with those of patients with AIDS and disseminated M. avium complex (MAC) infection (n = 24). Abdominal pain was seen more frequently in the group of patients infected with M. genavense than in(More)
OBJECTIVES The urethral trauma after catheterization with intermittent catheters was studied histologically using unconscious rabbits. SETTING The study was performed at Astra Hässle, Mölndal, Sweden. MATERIALS AND METHODS Fifteen rabbits were randomized into five groups (three rabbits in each group), one control group and four groups catheterized with(More)
In this paper we answer the following question: given a loopless symmetric digraph D with underlying interval graph H. what conditions are necessary and sufficient for the competition graph of D to be interval or unit interval‘? This question, first posed by Raychaudhuri and Roberts [lo]. was left open in our previous paper 171. In that paper we presented(More)
The domination graph of a digraph has the same vertices as the digraph with an edge between two vertices if every other vertex loses to at least one of the two. Previously, the authors showed that the domination graph of a tournament is either an odd cycle with or without isolated and/or pendant vertices, or a forest of caterpillars. They also showed that(More)