Constraint-Based Scheduling: Applying Constraint Programming by Philippe Baptiste

By Philippe Baptiste

Constraint Programming is a problem-solving paradigm that establishes a transparent contrast among pivotal points of an issue: (1) an actual definition of the restrictions that outline the matter to be solved and (2) the algorithms and heuristics permitting the choice of choices to resolve the matter.
for the reason that of those functions that Constraint Programming is more and more being hired as a problem-solving software to resolve scheduling difficulties. as a result the advance of Constraint-Based Scheduling as a box of analysis.
the purpose of this booklet is to supply an summary of the main commonplace Constraint-Based Scheduling recommendations. Following the rules of Constraint Programming, the ebook contains 3 certain components:

  • the 1st bankruptcy introduces the elemental ideas of Constraint Programming and gives a version of the limitations which are the main frequently encountered in scheduling difficulties.
  • Chapters 2, three, four, and five are curious about the propagation of source constraints, which generally are answerable for the "hardness" of the scheduling challenge.
  • Chapters 6, 7, and eight are devoted to the answer of a number of scheduling difficulties. those examples illustrate the use and the sensible potency of the constraint propagation equipment of the former chapters. additionally they exhibit that in addition to constraint propagation, the exploration of the hunt house needs to be rigorously designed, considering particular homes of the thought of challenge (e.g., dominance family members, symmetries, attainable use of decomposition rules).

bankruptcy nine mentions a number of extensions of the version and provides promising study directions.

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Example text

Earliest start times and earliest end times are adjusted inside the inner loop (lines 25, 32 and 23, 30). 3). 3 applies to the new algorithm. Let us now assume that Ai can be interrupted. It is proven in [6] that the earliest time at which Ai could end if all the other activities could be interrupted is equal to the maximal value of rnu{Ad + Pnu{Ai} for n triggering the Edge-Finding rules. The earliest end times computed by the new algorithm are, when they are used, equal to rnu{Ad + Pnu{Ai} for such n.

If n activities require the resource, the constraint can be implemented as n(n - 1)/2 (explicit or implicit) disjunctive constraints. As for Time-Table constraints, variants exist in the literature [66, 35, 68, 102, 146, 157, 14], but in most cases the propagation consists of maintaining arc-B-consistency on the formula: Enforcing arc-B-consistency on this formula is done as follows: Whenever the earliest end time of Ai exceeds the latest start time of A j , Ai cannot precede Aj; hence Aj must precede Ai.

Ar, A~, with each A~ forced to execute over /LB~ and A~ with the same earliest start time and latest end time as Ai and a processing time equal to m Pi - L length(ILBD 1=1 where length(ILBD denotes the length of the interval /LB~. • When Ai can be interrupted and either Ti + P = dk or H = dk in the course of the algorithm, it is certain that Ai cannot start before dk . Hence, the algorithm can also be used to update earliest start times of interruptible activities. Remark. When Ai has a fixed processing time and cannot be interrupted, the computation and the use of Ci and C to compute max (Tn' 0#0'<;;;0 + pO') serves only to avoid repeated iterations of the algorithm.

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