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BUG: spatial.distance: validate VI shape in pdist and cdist for metric='mahalanobis' - #26540
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…c='mahalanobis' Validate that kwargs['VI'] has shape (n, n) in _validate_mahalanobis_kwargs, matching the observation dimension and preventing buffer over-reads and silent arithmetic errors in compiled distance kernels. Closes scipygh-26526
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This is now causing linting errors on main @j-bowhay |
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Reference issue
Closes gh-26526 (Supersedes closed gh-26532 with required AI disclosure)
What does this implement/fix?
In
scipy.spatial.distance,pdistandcdistwithmetric='mahalanobis'did not validate that the inverse covariance matrixVIhas shape(n, n), wherenis the dimension of the observations.Because the underlying C kernel in
distance_impl.hlinearly indexescovinv + (i * n), passing an incompatible shape resulted in readingVIwith the wrong stride, while an undersized buffer resulted in reading past the allocated memory and terminating with a segmentation fault.This PR adds shape validation in
_validate_mahalanobis_kwargsensuringkwargs['VI'].shape == (n, n), consistent with the checks inscipy.spatial.distance.mahalanobis, and adds regression tests for bothcdistandpdist.Additional information
No compiled code is touched; this is pure Python parameter validation.
AI Generation Disclosure
AI tools (Antigravity) were used to assist with navigating the codebase, inspecting the C-level distance implementation, and drafting the shape check and pytest assertions. The mathematical requirements and regression tests were reviewed, verified, and run locally by the contributor before submission.