Release PyGAD 3.9.1

[ahmedfgad]

PyGAD 3.9.1

Release Date: October 16, 2026.

1. Roulette wheel selection and stochastic universal selection favor the better solutions when fitness values are negative. Before this change, each share was the fitness divided by the total, which flips the order for negative values: the fitness values -1 and -9 gave the worse solution 90% of the selections. Negative fitness values are now shifted by the smallest fitness first, so -1 and -9 become 8 and 0. This also covers mixed positive and negative values, and equal negative values give every solution the same chance. Fitness values that are all zero or above keep their exact previous behavior.
2. Regression tests cover negative, mixed-sign, equal negative, multi-objective, and large Python integer fitness, and a minimization run with each selector. The pygad.utils submodule version is 1.5.11.

[github-actions]

📊 Change summary

6 files changed · +188 / −14 lines

pie showData
    title Lines changed per file (202 total)
    "tests/test_probability_selection_negative_fitness.py" : 127
    "pygad/utils/parent_selection.py" : 60
    "docs/source/releases.md" : 7
    "docs/source/utils.md" : 4
    "pygad/_version.py" : 2
    "pygad/utils/__init__.py" : 2

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Per-file breakdown

File	+	−	total
tests/test_probability_selection_negative_fitness.py	127	0	127
pygad/utils/parent_selection.py	48	12	60
docs/source/releases.md	7	0	7
docs/source/utils.md	4	0	4
pygad/_version.py	1	1	2
pygad/utils/__init__.py	1	1	2
Total (6 files)	188	14	202