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Bug in NSGA-II in jMetal 5.8+: getting solutions from population during reproduction

See original GitHub issue

I was reading the code of NSGA-II and found out that, during reproduction, the solutions are taken sequentially from the population itself instead of the mating pool. See line 122:

https://github.com/jMetal/jMetal/blob/831d62d0bbf384e1770efc1bb6eef69ce0ce75b9/jmetal-algorithm/src/main/java/org/uma/jmetal/algorithm/multiobjective/nsgaii/NSGAII.java#L113-L125

I believe it is a bug, because the mating pool is the one containing the selected parents from the selection phase. Moreover, the indexes are taken from the mating pool, which is another indication that the reproduction is using the wrong list.

If it is indeed a bug (I might be wrong), the fix is straightforward: matingPool.get(i+j) instead of population.get(i+j) in line 122.

This code is the same for versions 5.7 and 5.9 too.

Issue Analytics

State:
Created 3 years ago
Comments:5 (5 by maintainers)

Top GitHub Comments

1reaction

ajnebrocommented, Jun 17, 2020

Thanks for reporting the bug and the pull request to fix it.

0reactions

GiovaniGuizzocommented, Jul 28, 2020

I guess since the fix from my pull request was merged into the 5.10 release, this issue can be closed.

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