Op 19-12-11 15:04, Patrik Dufresne schreef:
Hi Geoffrey,
Thanks for your opinion. I will try to implement what I call a
HardAndSoftPriorityScoreDefinition and give it back to the community.
Where is the best place to post a 'patch' ?
Create a pull request :) on http://github.com/drools-planner
https://github.com/droolsjbpm/droolsjbpm-build-bootstrap/blob/master/README.md
Design wise, I recommend:
It's basically about allowing a dynamic number of levels, instead of
just 2 (hard and soft).
it should not extend AbstractHardAndSoftScore, just extend AbstractScore
Because it cannot correctly implement HardAndSoftScore.getSoftScore();
I should just have a Map<Integer, Integer> levelToScoreMap; (no int
hardScore or int softScore)
hardScore is like level 0.
softScore is like level -1.
This allows for:
softerScore at level -2
harderScore at level 1
Higher level is more important then lower level.
The class name should probably contain the word "Level".
2011/12/19 Geoffrey De Smet <[email protected]
<mailto:[email protected]>>
Op 14-12-11 18:40, Patrik Dufresne schreef:
Hi,
I'm still in process to model my planning problem and I have some
difficulties in defining the correct weight of soft constraints.
I have soft constraints with different priorities : C1, C2, C3,
..., Cn where C1 are higher then C2. Currently, I've tried to set
different weight for each of them : C1 get higher weight. But
it's not sufficient since multiple C2 may balance one C1. What I
really need is to set the priority to every soft constraints.
Solution #1 :
My first thought it to implement a new score definition
(HardAndSoftPriorityScoreDefinition) having separate soft score
for each priority. The rule may insert ConstraintOccurence by
defining the weight and the priority. This solution seems elegant
but require effort to implement the score definition, the score
calculation, and other things I don't even know about.
That is the perfect solution to your problem. Start by copy
pasting DefaultHardAndSoftScoreDefinition and work your way from
there.
You'll need to create at least a ScoreDefinition, ScoreCalculator
and Score.
I've been thinking about adding such a "dynamic" score definition
to planner's build-in scores,
but so far every use case where the developers said they needed
this, it turned out end-users meant it differently:
when you break a 100 C2's, then it's better to break 1 C1 instead...
Solution #2 :
The other solution is stated in the Drools Planner User Guide :
"Most use cases will also weigh their constraints
differently, by multiplying the count of each score rule with
its weight. For example in freight routing, you can make 5
broken "avoid crossroads" soft constraints count as much as 1
broken "avoid highways at rush hour" soft constraint. This
allows your business analysts to easily tweak the score
function as they see fit."
Even tough I don't know how to implement this, it's seems much
easier to achieve since it's only a rule. Compare to solution #1,
it's lack the support of soft constraints with same priority but
different weights.
That text describes plain-old weighting. Say C1 weights 100 and C2
weights 2, then you can break 50 C2's for every 1 broken C1.
This is far easier and most of the time end-users actually mean this.
Make exaggerated examples (1000 C2's broken vs 1 C1 broken) and
make your end-users decide what they prefer. If they still prefer
1000 C2's broken, then you need #1.
Tip: Sometimes, taking the square of a weight is a neat trick.
In bin packing, say you got
Solution A with 3 CPU and 3 CPU too little = 3² + 3² = 18
and Solution B with 4 CPU and 2 CPU too little = 4² + 2² = 20
So the second is worse even though they both miss 6 CPU.
What is your opinion about both solution.
Is one faster then the other ?
Is it hard to create a new score definition ?
Did anyone ever did this ?
--
Patrik Dufresne
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With kind regards,
Geoffrey De Smet
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Patrik Dufresne
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With kind regards,
Geoffrey De Smet
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