如何在Optaplanner中使用最小冲突算法

Question

Is there a min-conflict algorithm in optaplanner? or how to do it?

What about using it as part of the neighborhood selection like:

1. Define custom swap factory that construct neighborhood as follow
2. Get all violations per variable to optimize, thus requires a call to scoreDirector.calculateScore then parse/process constraintMatches
3. Order by variables lowest score or highest violations
4. Construct neighborhood via swapping those variables first

If that's viable, is there a way to get the constraintMatches without the need to re-call the calculateScore in order to speed up the process

Answer 1

This algorithm isn't supported out of the box yet by OptaPlanner. I 'd call it Guided Local Search . But it's not that hard to add yourself. In fact, it's not a matter of changing the algorithm, but changing the entity selectors.

Something like this should work:

<swapMoveSelector>
  <entitySelector>
    <cacheType>STEP</cacheType>
    <probabilityWeightFactoryClass>...MyProbabilityWeightFactory</probabilityWeightFactoryClass>
  </entitySelector>
</swapMoveSelector>

Read about the advanced swapMoveSelector configuration , entity selector , sorted selection and probability selection .

The callback class you implement for the probabilistic selection or sorted selection should prioritize entities that are part of a conflict.

I would definitely use sorted or probabilistic selection on the entity selector, not the entire swapMoveSelector because that is overkill, cpu hungry and memory hungry.

I would prefer probabilistic selection over sorted selection. Even though sorted selection better reflects your pseudo code, I believe (but haven't proven) that probabilistic selection will do better, given the nature of Metaheuristics. Try both, run some benchmarks with the Benchmarker and let us know what works best ;)

Answer 2

Not sure about how to solve your overall problem but for your last point:

You can create a PhaseLifecycleListener and attach it via ((DefaultSolver) solver).addPhaseLifecycleListener

In the stepStarted or stepEnded(depending on your need) you can then call

stepScope.getScoreDirector().getConstraintMatchTotals()

to get the constraint totals.

Hope this somewhat helps.