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Improving intervals1

Published online by Cambridge University Press:  07 November 2008

W. Ken Jackson
School of Computing Science, Simon Fraser University, Burnaby, British Columbia, CanadaV5A 1S6 (e-mail:
F. Warren Burton
School of Computing Science, Simon Fraser University, Burnaby, British Columbia, CanadaV5A 1S6 (e-mail:
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We show how improving values (Burton, 1991) can be extended to handle both upper and lower bounds. The result is a new data type, called improving intervals. We give a simple implementation of improving intervals that uses a list of successively tighter bounds to represent a value. A program using improving intervals can be evaluated as a parallel program using speculative evaluation. The utility of improving intervals is demonstrated through two programs: parallel alpha-beta and parallel branch-and-bound

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