Sweep Synchronization as a Global Propagation Mechanism

Beldiceanu, Nicolas and Carlsson, Mats and Thiel, Sven (2003) Sweep Synchronization as a Global Propagation Mechanism. [SICS Report]



This paper presents a new generic filtering algorithm that simultaneously considers n conjunctions of constraints as well as those constraints mentioning some variables Yk of the pairs X,Yk (1<=k<=n) occurring in these conjunctions. The main benefit of this new technique comes from the fact that, for adjusting the bounds of a variable X according to n conjunctions, we do not perform n sweeps in an independent way but rather synchronize them. We then specializes this technique to the non-overlapping rectangles constraint where we consider the case where several rectangles of height one have the same X coordinate for their origin as well as the same length. For this specific constraint we come up with an incremental bipartite matching algorithm which is triggered while we sweep over the time axis. We illustrate the usefulness of this new pruning method on a timetabling problem, where each task can’t be interrupted and requires the simultaneous availability of n distinct persons. Each person has its own periods of unavailability and can only perform one task at a time.

Item Type:SICS Report
Uncontrolled Keywords:Constraint Programming, Non-overlapping, Sweep, Timetabling
ID Code:2314
Deposited By:Vicki Carleson
Deposited On:29 Oct 2007
Last Modified:18 Nov 2009 16:05

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