How to define constraint about consecutive periods in optaplanner

Question

In my optaplanner project i have periods with fixed duration. For some of them there is a medium constraint that they should be scheduled in a row, occupying for example 5 directly adjacent timeslots. I want to use Java constraints streams but dont manage to define this constraint using the timeslot-pattern.

I know that this constraint can be defined using the time-grain-pattern as suggested by https://stackoverflow.com/a/30702865. I have done this and it works. But I want to compare timeslot-pattern to time-grain-pattern because the have different behaviour when it comes to escape local maxima. The problem with time-grain-pattern is that those 5 periods could also be sheduled in every possible partition of 5 (eg. as 2 + 2 + 1).

Has anyone a hint on how to define the constraint using timeslot-pattern?

You got any solution of this, if yes then please help me for the same. — Keyur Bhanderi, Feb 02 '22 at 13:15

score 2 · Answer 1 · answered Feb 25 '20 at 08:22

You may want to try using the newly added ifExists() building block. Without knowing your actual domain model, I imagine the constraint to look like this:

private Constraint twoConsecutivePeriods(ConstraintFactory constraintFactory) {
    return constraintFactory.from(Period.class)
            .ifExists(Period.class, equal(Period::getDay, period -> period.getDay() + 1))
            .penalize("2 consecutive periods", period -> ...);
}

Consequently, ifNotExists() may be used to achieve the opposite. We have examples of both in Traveling Tournament OptaPlanner example.

Please note that this API is only available since OptaPlanner 7.33.0.Final onward.

score 0 · Answer 2 · answered Feb 03 '22 at 20:34

I solved the problem using ConstraintCollectors.toList() as follows:

factory.from(Period.class).groupBy(Period::getCourse, ConstraintCollectors.toList())
                    .penalize(id, score, (course,list)->dayDistributionPenalize(course,list));

and

public int dayDistributionPenalize(Course course, List<Period> list) {
        var penalize = 0;
        var dayCodes = dayCodesFromPeriodList(list);

        for (var dayCode : dayCodes)
            if (!getAllowedDayCodes(course).contains(dayCode))
                penalize++;
        return penalize;
    }

Where getAllowedDayCodes() returns for example 0111110000, 0230000000 or 0005000000 etc. from a hash-map if a course has to have 5 consecutive periods.

How to define constraint about consecutive periods in optaplanner

2 Answers2