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ILOG OPL Development Studio Language Reference Manual

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Precedence constraints between interval variablesPrecedence constraints are common scheduling constraints used to restrict the relative positionof interval variables in a solution.For example a precedence constraint can model the fact that an activity a must end beforeactivity b starts (optionally with some minimum delay z). If one or both or the interval variablesof the precedence constraint is absent, then the precedence is systematically considered to betrue; therefore it does not impact the schedule.More formally, the semantics of the relation TC( , , z) on a pair of fixed intervals , andfor a value z depending on the constraint type TC is given in the following table.For syntax and examples, see the following functions described in the <strong>OPL</strong> <strong>Language</strong> Quick<strong>Reference</strong>. Note that none of these constraints may be used in a meta-constraint.♦endAtEnd♦endAtStart♦endBeforeEnd♦endBeforeStart♦startAtEnd♦startAtStart♦startBeforeEnd♦startBeforeStartI L O G O P L D E V E L O P M E N T S T U D I O L A N G U A G ER E F E R E N C E M A N U A L153

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