BUG: optimize.differential_evolution: fix division by zero error

[stepeos]

Reference issue

Closing possible division by zero bug #18388

What does this implement/fix?

Adding the machine epslion after taking the absolute to avoid division by zero.

[mdhaber]

Thanks @stepeos @ChVeen.
Is there a test problem that would experience the divide by zero without this patch and is fixed by this patch? It would be good to add that as a unit test in scipy/optimize/tests/test__differential_evolution.py following the style of test_gh_4511_regression, which identifies what the test is for in a comment.
Adding that would make it easy for @andyfaff, the author, to review and merge.
(BTW, in the future, please open PRs from a feature branch rather than your main.)

[andyfaff]

Thanks for this PR.

Yes, it was to prevent division by zero. Having a mean population energy of zero is not unknown, but I doubt the bug would've seriously bitten anyone.

As @mdhaber says, testing for regressions is an important part of the project. However, in this case I'm sufficiently confident that the fix is straightforward to permit a merge without it.

The reason a feature branch is important is that it allows your fork/main to be updated easily without issues, allowing you to work on many independent feature branches without them interfering with each other.

There are also guidelines for how to construct commit messages at https://docs.scipy.org/doc/scipy/dev/contributor/development_workflow.html#writing-the-commit-message.

[andyfaff]

Merging without CI running, it's a simple one-liner and I checked bracket pairing locally.