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- Ryan B. Hayward
- J. Comb. Theory, Ser. B
- 1985

A graph is triangulated if it has no chordless cycle with four or more vertices. It follows that the complement of a triangulated graph cannot contain a chordless cycle with five or more vertices. We introduce a class of graphs (namely, weakly triangulated graphs) which includes both triangulated graphs and complements of triangulated graphs (we define a… (More)

- Russell Greiner, Ryan B. Hayward, Magdalena Jankowska, Michael Molloy
- Artif. Intell.
- 2006

Many tasks require evaluating a specified Boolean expression over a set of probabilistic tests whose costs and success probabilities are each known. A strategy specifies when to perform which test, towards determining the overall outcome of . We are interested in finding the strategy with the minimum expected cost. As this task is typically NP-hard — for… (More)

- Broderick Arneson, Ryan B. Hayward, Philip Henderson
- IEEE Transactions on Computational Intelligence…
- 2010

Hex, the classic board game invented by Piet Hein in 1942 and independently by John Nash in 1948, has been a domain of AI research since Claude Shannon's seminal work in the 1950s. Until the Monte Carlo Go revolution a few years ago, the best computer Hex players used knowledge-intensive alpha-beta search. Since that time, strong Monte Carlo Hex players… (More)

- Ryan B. Hayward, Jeremy P. Spinrad, R. Sritharan
- SODA
- 2000

We use the notion of handle, introduced by Hayward, to improve algorithms for weakly chordal graphs. For recognition we reduce the time complexity from O(n2m) to O(rn 2) and the space complexity from O(n 3) to O(n + m), and also produce a hole or antihole if the input graph is not weakly chordal. For the optimization problems clique, independent set,… (More)

- Colin McDiarmid, Ryan B. Hayward
- J. Algorithms
- 1996

Let Qn be the random number of comparisons made by quicksort in sorting n distinct keys, when we assume that all n! possible orderings are equally likely. Known results concerning moments for Qn do not show how rare it is for Qn to make large deviations from its mean. Here we give a good approximation to the probability of such a large deviation, and find… (More)

- Ryan B. Hayward, Chính T. Hoàng, Frédéric Maffray
- Graphs and Combinatorics
- 1989

- Ryan B. Hayward, Ron Shamir
- Discrete Applied Mathematics
- 2004

A graph G=(V; E) is a tolerance graph if there is a set I={Iv | v∈V} of closed real intervals and a set ={ v | v∈V} of positive real numbers such that (x; y)∈E ⇔ |Ix∩ Iy|¿min{ x; y}. We show that every tolerance graph has a polynomial size integer representation. It follows that tolerance graph recognition is in NP. c © 2004 Elsevier B.V. All rights… (More)

BACKGROUND
Ischemia followed by reperfusion in the presence of polymorphonuclear leukocytes (PMNs) results in cardiac contractile dysfunction as well as cardiomyocyte injury. These deleterious effects are due in large part to endothelial dysfunction leading to the upregulation of cell adhesion molecules and subsequent neutrophil-endothelium interaction. At… (More)

- T O Nossuli, R Hayward, R Scalia, A M Lefer
- Circulation
- 1997

BACKGROUND
Peroxynitrite (ONOO-) is purported to exert cytotoxic effects at high doses. However, physiologically relevant concentrations of ONOO- inhibit polymorphonuclear neutrophil (PMN) adhesion to the endothelium and attenuate PMN-mediated contractile dysfunction in isolated perfused rat hearts. We are unaware of any reports in vivo showing effects of… (More)

In 1981 Claude Berge asked about combinatorial properties that might be used to solve Hex puzzles. In response, we establish properties of dead, or negligible, cells in Hex and the Shannon game. A cell is dead if the colour of any stone placed there is irrelevant to the theoretical outcome of the game. We show that dead cell recognition is NPcomplete for… (More)