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I tested out the examination example of Drools Planner. After a while I wanted to solve a unsolved problem. I started the app, selected an xml-file and hit the solve button. In my XML file were 5 exams with 5 different topics (t1, t2, t3, t4, t5).

Drools generated a solution. In this solution are 5 exams but all of them have the same type of topic (t1). I don't find the failure why drools give me 5 exams with the same topic. At the beginning (before solving) the debugger tells me that all exams have different topic.

Normally the topic of an exam shouldn't be changed.

In my ExaminationSolutionInitializer.java the methhod "changeWorkingSolution" returns a the wrong Solution. scoreDirector.getWorkingSolution() generated the exams with only one topic.

Could anybody help me?

Vivid
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3 Answers3

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There's probably a bug in your XML input file. Can you copy paste it here or on gist.github.com and link it?

In Drools Planner's examination example, each Exam instance has exactly 1 field Topic and it is never changed by Planner. It's the Exam's field Room and Period that are changed by Planner.

public class Exam ... {

    private Topic topic;
    ...

    // Planning variables: changes during planning, between score calculations.
    private Period period;
    private Room room;
    ...
}

Also, the Exam to Topic relation is a 1 to 1 relation. They could have been designed as 1 class, but haven't. The Topic class holds all the exam info that don't change during planning, the Exam class links each Topic which it's Room and Period.

examination domain diagram

As for the ExaminationSolutionInitializer.java: That was written before the construction heuristics were added in Planner. Now, it's usually better to just use first fit or first fit decreasing instead. The only reason it's still there in the examination example, is because it has domain specific code to deal with the Exam.isCoincidenceLeader() case when multiple exams need to be scheduled at the same period and therefore need to be moved together.

Geoffrey De Smet
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Problem was that I declared topic as a @PlanningVariable in my exam.java

Vivid
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    Interesting :) I guess you also declared a valid @ValueRange. I wonder if there's any way that Planner can detect such a problem? For many common mistakes, it automatically fails-fast, but for this one I don't think it can? – Geoffrey De Smet Aug 09 '12 at 07:25
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    Don't ask me why I did it ;-) But a detection like you mentioned would be very helpful. Maybe an output on the console including all the PlanningVariables would be an idea. The user should see which entity is the planning Entity and which static and planning variables it has. :) – Vivid Aug 09 '12 at 22:06
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Maybe the problem is my new planningVariable "day". I didn't want to have a day index in the period. So I copied the period classes and made them to day classes. In my ExaminationSolutionInitializer I have the inititalizeExamList. Before looping over every period and every ExamToHandle, I loop over the days. But I think the problem could be scheduleLeader(). In this method I figure out the bestRoom and the bestPeriod, but no bestDay. What do you think?

Vivid
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