Some extra info, on top of Reinis's excellent advice:
Take a look at this image:
https://hudson.jboss.org/hudson/view/Drools%20jBPM/job/drools-planner/lastSuccessfulBuild/artifact/drools-planner-docs/target/docbook/publish/en-US/html_single/images/Chapter-Optimization_algorithms/generalPhaseSequence.png
As the image shows, <constructionHeuristics> don't result into an
optimal solution.
You need to do <localSearch> after it too.
Oversimplifiedly speaking, Construction heuristics are fast and brittle,
Local Search is slow and robust.

Only construction heuristics *_FIT_DECREASING use
difficultyWeightFactoryClass.
By giving a better estimation of the planning difficulty of a entity,
the construction heuristics perform better and Local Search has to do
less work for the same result.

Read these sections in the manual:
Without difficultyWeight:
http://docs.jboss.org/drools/release/5.5.0.Final/drools-planner-docs/html_single/index.html#d0e6076
With difficultyWeight (the result of FFD is statistically better than FF):
http://docs.jboss.org/drools/release/5.5.0.Final/drools-planner-docs/html_single/index.html#d0e6126
DifficultyWeight details:
http://docs.jboss.org/drools/release/5.5.0.Final/drools-planner-docs/html_single/index.html#planningEntityDifficulty

Op 07-01-13 22:04, Reinis schreef:
> Hello Michiel,
>
>  >I thought it was used to indicate which PlanningEntities to handle
> first in order to get faster to a solution.
>
> To my understanding this is not quite true. DifficultyWeight defines
> what Entities will likely be more difficult to plan, period.
>
> What is actually DONE with this statement (of difficulty) is decided by
> meta heuristics algorithm and/or by different selectors (not sure about
> this one though). What I am saying
> - difficulty weight just says "yo, dude, this planning entity is
> hard/easy to plan"
> - meta heuristics algorithm (also construction heuristics) then say "oh
> great, then I start with easy ones" or "oh dude, then I get first down
> to hard ones" or even "nice, but I don't give a damn about difficulty
> whatdoyaknow"
>
> *assumption mode on*
> The reason why you all of the sudden get negative hard score MIGHT be
> that the "right" entities are falling out of the selection. And this is
> controlled by meta heuristics algorithm.
>
> As I understand all the meta heuristics magic - it can solve problems
> with the space of 10^650 because... it cheats! Yes, it does not evaluate
> ALL of the possible values (entities or planning variables) but selects
> a subset of those (the ones likely to yield a solution).
>
> And one more thought - changing difficulty weight calculation (in
> factory) should normaly NOT have such a drastic influence on score (up
> to now I used difficulty weight calcs to increase performance). So I am
> suggesting here that the issue MAY lay some other place (typical would
> be local optima).
> *assumption mode off*
>
> In drools planner docs there is some decent information on selection of
> stuff. If I may suggest, start with construction heuristic types and
> check out the docs where it says what BEST_FIT or, respectively,
> BEST_FIT_DECREASING does.
>
> I hope I could at least give you couple of ideas on where to proceed
> with the issue.
>
> br
> Reinis
>
> On 01/07/2013 09:26 PM, Michiel Vermandel wrote:
>> Hi,
>>
>> I am struggling with the purpose of difficultyWeightFactoryClass in
>> the @PlanningEntity annotation.
>>
>> I thought it was used to indicate which PlanningEntities to handle
>> first in order to get faster to a solution.
>> Though it seems that it also has impact on whether or not to get to a
>> zero-hardscore solution.
>> I mean I have a testcase that resolves to a zero-hardscore solution.
>> Then I change something small in how the difficultyWeightFactoryClass
>> calculates the weight and all the sudden I get a negative-hardscore
>> solution.
>> I thought it would still get to the same zero-hardscore solution but
>> in a shorter solving time.
>>
>> My solver termination is as follows:
>>
>> <termination>
>> <terminationCompositionStyle>OR</terminationCompositionStyle>
>> <maximumSecondsSpend>3600</maximumSecondsSpend>
>> <scoreAttained>0hard/0soft</scoreAttained>
>>      </termination>
>>
>> and constructionHeuristic:
>>
>> <constructionHeuristic>
>> <constructionHeuristicType>BEST_FIT_DECREASING</constructionHeuristicType>
>>      </constructionHeuristic>
>>
>> I do not reach a zero-hardscore and the time spent is about 2.8 seconds...
>>
>> If I read the best solution I get:
>> .isEveryProblemFactChangeProcessed(): true
>> .isTerminateEarly(): false
>>
>> Any idea why I do not get a zero-hardscore solution anymore when only
>> making a small change to the difficultyWeightFactoryClass logic?
>>
>> Thanks
>>
>> Michiel.
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