GeezerVison

[DOC] Fix the shrinking default documented for svm._libsvm.cross_validation

Reference Issues/PRs

None — found while auditing the docstring/code consistency of the SVM Cython bindings.

What does this implement/fix? Explain your changes.

sklearn/svm/_libsvm.pyx documents a default for shrinking that the binding does not have. In cross_validation:

 753:     int shrinking=0,          # signature default
 815:     shrinking : int, default=1   # docstring default

The docstring was evidently carried over from libsvm in the same file, where shrinking really does default to 1 (signature line 64, docstring line 122 — those two agree). cross_validation is the only binding in the file whose documented default disagrees with its signature, and probability, cache_size, max_iter, tol and random_seed all agree.

This PR changes only the documented default (line 815) to 0, so the docstring matches the signature. No behaviour changes.

Was the behavior checked?

• inspect.signature(sklearn.svm._libsvm.cross_validation).parameters["shrinking"].default == 0, while inspect.getdoc(...) prints shrinking : int, default=1 — measured on installed scikit-learn 1.9.1 and 1.7.2 wheels.
• On a 2500-sample RBF problem, cross_validation with the default, with shrinking=0 and with shrinking=1 produced identical predictions (shrinking is a solver optimisation, not a model choice), so this is a documentation-only correction.
• The only in-tree caller is sklearn/svm/tests/test_svm.py, which omits shrinking and so runs with the heuristic disabled while the docstring advertises it as enabled.

Any adverse effects / open question

I am deliberately not changing the default: making cross_validation inherit libsvm's shrinking=1 would be a behaviour change in an internal binding whose callers currently get shrinking off, and that deserves a maintainer decision. If the intent was 1, the fix belongs in the signature, and this docstring change should be dropped in favour of that. Happy to convert this into a close-style cleanup of the stale docstring if maintainers prefer.

Checks

• I have run the linter and pre-commit hooks locally (single docstring line in a .pyx file).
• No public API, default value or behaviour is changed by this PR.