tailieunhanh - Báo cáo tin học: "Dominating sets of random 2-in 2-out directed graphs"

Tuyển tập các báo cáo nghiên cứu khoa học về toán học trên tạp chí toán học quốc tế đề tài: Dominating sets of random 2-in 2-out directed graphs. | Dominating sets of random 2-in 2-out directed graphs Stephen Howe Department of Mathematics and Statistics University of New South Wales Sydney NSW 2052 Australia stephenh@ Submitted Aug 8 2007 Accepted Jan 30 2008 Published Feb 11 2008 Mathematics Subject Classifications 05C80 05C69 05C20 Abstract We analyse an algorithm for finding small dominating sets of 2-in 2-out directed graphs using a deprioritised algorithm and differential equations. This deprioritised approach determines an . upper bound of on the size of the smallest dominating set of a random 2-in 2-out digraph on n vertices. Direct expectation arguments determine a corresponding lower bound of . 1 Introduction A directed multigraph G is a set V V G of vertices with a multiset E E G c V X V of directed edges. When E contains no repeated edges and no loops edges of the form v v for some v 2 V we say that G is simple and call G a directed graph or digraph. The in-degree of a vertex u 2 V is the number of edges of the form v u for some v 2 V the out-degree of u is the number of edges of the form u v for some v 2 V. We consider only directed multigraphs simple or otherwise for which every vertex has in-degree 2 and out-degree 2. Such graphs are called 2-in 2-out or 2-regular. A random 2-in 2-out digraph on n vertices is a digraph chosen uniformly at random from the set of all 2-in 2-out digraphs on n vertices. Often the probability of a random graph having a certain property such as being connected tends to 1 as n tends to infinity. In this case we say that a random graph has such a property asymptotically almost surely . . For example . a random 2-in 2-out digraph is connected 3 . In 5 Duckworth and Wormald determined . upper and lower bounds for dominating sets of random cubic graphs. We determine similar bounds for random 2-in 2-out digraphs. Research supported by the ARC Centre of Excellence for Mathematics and Statistics of Complex Systems MASCOS .

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