[rules-users] Continuous Planning values for task planning
Josef Bajada
josef.bajada at gmail.com
Fri Aug 17 19:53:44 EDT 2012
Hi Geoffrey,
Following your advice and after gaining some more understanding of planner,
I think approaching the problem as a chain of tasks one of the other makes
sense. It would have some 'wait' time between tasks where the end time of
the previous task is smaller than the minimum time the task has to wait
after its dependency (which could be different from the previous task).
I've noticed that in most examples (TSP and VRP), there is some separation
between the model and the planning entity that is being moved around in the
chain, which also makes sense. (For instance in TSP, Visit is the planning
entity while City is the data entity). When the planning entity gets
cloned, the data entity gets assigned to the clone.
I am concerned however, that with my dependency between tasks and their end
times (which are as such a property of the planning entity not the data
entity) I won't be able to model them in this way. (For a task to know
whether it has violated its hard constraint it needs to get access to the
end time of its dependency, which is in the planning entity). My concern is
that I might end up with a whole mess when it comes to the cloning of
tasks. I am also concerned about the performance of computing the end time
of each node recursively based on its previous task and dependent tasks.
What is the best approach in this case?
thanks,
Josef
On 25 July 2012 08:30, Geoffrey De Smet <ge0ffrey.spam at gmail.com> wrote:
>
> Op 24-07-12 23:14, Josef Bajada schreef:
>
> Hi Geoffrey,
>
> Thanks for your reply.
>
> > Does it make sense to wait longer than 7 mins after task A (presuming
> no other task forces occupies the user at that time)?
> > Put differently: Can we say that the starting time of B =
> Math.max((endTime of task before B), (endTime of task A + 7 minutes))?
> > If we can say that, it's pointless to investigate the solutions where
> task B starts 8 minutes after task A and the user doing no task that last
> minute.
>
> Yes, the starting time of B = Math.max((endTime of task before B),
> (endTime of task A + 7mins)) as long as it is smaller than (endTime of task
> A + 8mins).
> Yes, it is pointless to investigate the solutions where task B starts 8
> minutes after task A and the user doing no task that last minute.
> The 8 minute is just a constraint that the task in between tasks A and B
> cannot take longer than 7:59s.
>
> I am thinking that maybe instead of using time itself as the planning
> variable, we would use time just to determine the Hard and Soft scores.
> So if Task B is scheduled after Task A + 8mins by the solver, then it
> inflicts on the hard score. Similarly if Task B is scheduled before Task A
> + 7 mins.
> Does my reasoning make sense in any way?
>
> Yes, but personally, I 'd design it differently (although I have no proof
> that my way would be better), like this:
> "Task B is scheduled after Task A + 8mins by the solver" => make this a
> hard constraint
> "Task B is scheduled before Task A + 7 mins" => make this a build-in hard
> constraint (= not a constraint in the scoreDRL or ScoreCalculator, but by
> design, see manual).
> Each Task is assigned to a previousTaskOrPerson (and this variable is
> chained). It does not know it's startingTime directly.
> The scoreDRL or ScoreCalculator calculates the startingTime of a Task
> dynamically, by applying this logic:
> starting time of B = Math.max((endTime of previousTaskOrPerson of B),
> (endTime of task A + 7mins))
> Note: "Chained=true" guarantees that there are no cycles of Tasks and that
> no Tasks exists with a previousTaskOrPerson == null.
> Note: "(endTime of task A + 7mins)" is not hard coded in the score
> function: you won't find "7" or "A" in there.
>
>
>
> thanks,
> Josef
>
>
>
> On 24 July 2012 20:46, Geoffrey De Smet <ge0ffrey.spam at gmail.com> wrote:
>
>>
>> Op 23-07-12 16:26, Josef Bajada schreef:
>>
>> Hi Geoffrey,
>>
>> Well I want to leave 'space' between tasks in the situations where
>> there are hard constraints that require me to put this space.
>>
>> This makes the chaining technique harder to model, but I wouldn't write
>> it off yet.
>>
>>
>> As a simple example:
>>
>> Task A: Put pasta in boiling water (duration 40 seconds)
>> Task B: Take pasta out of boiling water (duration 50 seconds, cannot
>> start before 7 mins after Task A finishes, cannot start after 8 mins after
>> Task A finishes)
>>
>> Does it make sense to wait longer than 7 mins after task A (presuming no
>> other task forces occupies the user at that time)?
>> Put differently: Can we say that the starting time of B =
>> Math.max((endTime of task before B), (endTime of task A + 7 minutes))?
>> If we can say that, it's pointless to investigate the solutions where
>> task B starts 8 minutes after task A and the user doing no task that last
>> minute.
>> If we can say that, then chaining can calculate the the starting time of
>> a task on the fly differently.
>>
>> Task C: Chop vegetables (duration 2 minutes).
>>
>> This will evidently leave some gaps. The ideal result from the solver
>> should be:
>>
>> Task A: at time 0 (ends at 40s)
>> Task C: at time 41s (ends at 2:41)
>> Task B: at time 7:40
>>
>> There is a gap between C and B which is OK.
>>
>> If another Task is added to the story:
>> Task D: Prepare sauce (duration 7 minutes)
>>
>> I would want the following result:
>>
>> Task A: at time 0 (ends at 40s)
>> Task D: at time 41s (ends 7:41s)
>> Task B: at time 8:42s (ends 9:32s)
>> Task C: at time 9:33s (ends 11:33s)
>>
>> Task C can actually take place before Task A too.
>>
>> I still need to read and understand the chaining functionality
>> properly. Do you think it would allow me to achieve the above?
>>
>> I don't know.
>> But using continuous variables in a search problem such as this that
>> smells discrete with discrete constraints (A must start before B, ...),
>> could blow up the search space unnecessarily.
>>
>> If you want to look into using continuous variables: the support for it
>> is limited currently.
>> you can reuse the Drools Planner metaheuristic algorithms (including
>> termination, score, ...), but there's no decent generic move factory
>> support for continuous variables yet.
>> So you 'll have to write a custom MoveFactory that creates a limited
>> subset of moves.
>> Also, construction heuristics can't handle continuous variables yet, so
>> you 'll have to write a custom SolutionIntializer.
>> There are examples with a custom MoveFactory and a custom
>> SolutionIntializer where you can copy paste from, but none with continuous
>> variables at the moment.
>>
>> thanks,
>>
>> Josef
>>
>>
>>
>> On 22 July 2012 20:05, Geoffrey De Smet <ge0ffrey.spam at gmail.com> wrote:
>>
>>> Presuming that you don't want to leave space between tasks, you can
>>> design your model differently by using the "chained" functionality:
>>> it will be far more efficient and the planning variable won't be
>>> continuous.
>>>
>>> Let's presume you're scheduling Tasks to Persons.
>>>
>>> @PlanningEntity
>>> class Task implements TaskOrPerson {
>>>
>>> ...
>>>
>>> @PlanningVariable(chained = true)
>>> @ValueRanges({
>>> @ValueRange(type = ValueRangeType.FROM_SOLUTION_PROPERTY,
>>> solutionProperty = "taskList"),
>>> @ValueRange(type = ValueRangeType.FROM_SOLUTION_PROPERTY,
>>> solutionProperty = "personList",
>>> excludeUninitializedPlanningEntity = true)})
>>> public TaskOrPerson getPreviousTaskOrPerson() {
>>> return previousTaskOrPerson;
>>> }
>>>
>>> public int getDuration() {
>>> return duration;
>>> }
>>>
>>> public int getStartingTime() {
>>> int startingTime = 0;
>>> TaskOrPerson taskOrPerson = getPreviousTaskOrPerson();
>>> while (taskOrPerson instanceof Task) { // Every chain is
>>> guarantee to end up with an anchor (= Person)
>>> startingTime += ((Task) taskOrPerson).getDuration();
>>> taskOrPerson = ((Task)
>>> taskOrPerson).getPreviousTaskOrPerson()
>>> }
>>> return startingTime;
>>> }
>>>
>>> }
>>>
>>> class Person implements TaskOrPerson {
>>>
>>> }
>>>
>>> For a good example, take a look at the VehicleRouting example.
>>> For more info about chaining, in the manual see section 4.3.4.2.6.
>>> Chained
>>>
>>> http://docs.jboss.org/drools/release/5.4.0.Final/drools-planner-docs/html_single/index.html
>>>
>>> Op 22-07-12 18 <22-07-12%2018>:00, Josef Bajada schreef:
>>>
>>> Hi,
>>>
>>> I am new to Drools and Drools Planner, so apologies if I am asking
>>> anything obvious.
>>>
>>> My objective is to implement a simple (for now) planner which
>>> schedules tasks according to 2 main criteria:
>>> - Their duration (in seconds)
>>> - Their dependencies on other tasks (e.g. Hard Constraint that Task B
>>> has to start between 180 and 200 seconds after Task A finishes).
>>>
>>> Since there are gaps between dependent tasks as part of the hard
>>> constraints other tasks can be fitted in between dependent tasks.
>>> So the Solver needs to find the optimal start time for each task that
>>> satisfies the hard constraints, and in the shortest total timeline possible
>>> to complete all tasks (soft constraint).
>>>
>>> The main problem I am finding is that this start time, which is
>>> essentially the planning variable is a continuous variable.
>>> Chapter 4 of the Drools documentation mentions very briefly (Section
>>> 4.3.4.1) that planning variables can be continuous, but there does not
>>> seem to be any more details about how to achieve this.
>>>
>>> Even if the planning variable was discrete (say bins of 5 second
>>> intervals), there is no upper bound as such.
>>>
>>> How is it best to handle such planning variables in Drools Planner?
>>>
>>> thanks,
>>> josef
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> rules-users mailing listrules-users at lists.jboss.orghttps://lists.jboss.org/mailman/listinfo/rules-users
>>>
>>>
>>> --
>>> With kind regards,
>>> Geoffrey De Smet
>>>
>>>
>>> _______________________________________________
>>> rules-users mailing list
>>> rules-users at lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/rules-users
>>>
>>>
>>
>>
>> _______________________________________________
>> rules-users mailing listrules-users at lists.jboss.orghttps://lists.jboss.org/mailman/listinfo/rules-users
>>
>>
>> --
>> With kind regards,
>> Geoffrey De Smet
>>
>>
>> _______________________________________________
>> rules-users mailing list
>> rules-users at lists.jboss.org
>> https://lists.jboss.org/mailman/listinfo/rules-users
>>
>>
>
>
> _______________________________________________
> rules-users mailing listrules-users at lists.jboss.orghttps://lists.jboss.org/mailman/listinfo/rules-users
>
>
> --
> With kind regards,
> Geoffrey De Smet
>
>
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> rules-users mailing list
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