BUG: validate contraction axes in tensordot (#30521)#30700
Merged
charris merged 1 commit intonumpy:maintenance/2.4.xfrom Jan 21, 2026
Merged
BUG: validate contraction axes in tensordot (#30521)#30700charris merged 1 commit intonumpy:maintenance/2.4.xfrom
charris merged 1 commit intonumpy:maintenance/2.4.xfrom
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Backport of #30534.
tensordot performs a tensor contraction where each axis corresponds to a distinct summation index. Duplicate contraction axes (e.g. axes=([1, 1], [0, 0])) are mathematically invalid but currently fail later during an internal transpose, raising ValueError: axes don't match array. This PR adds early validation to reject duplicate axes explicitly, aligning the behavior with the definition of tensor contraction and other NumPy axis-handling APIs.
Current behavior:
Supplying duplicate contraction axes (e.g. axes=([1, 1], [0, 0])) causes tensordot to fail later during an internal transpose, raising ValueError: axes don't match array.
Expected behavior:
Duplicate contraction axes should be rejected explicitly, since tensor contraction requires distinct summation axes, and a clear input-validation error should be raised before any internal reshaping or transposition.