[0z5a]

Summary

zipped_product (cute-layout/src/algebra/tiling.rs), which backs blocked_product, raked_product and make_layout_tv, splits the block and the repetition layout returned by logical_product into modes and expects exactly one of each per axis. With one-axis inputs the repetition complement(a) ∘ b can have several flat modes, for example complement(3:2, 12) = (2,2):(1,6), so valid inputs fail with AlgebraError("product: unexpected mode structure"):

Call	main	this PR
blocked_product(3:2, 4:1)	error	(3,2,2):(2,1,6)
raked_product(3:2, 4:1)	error	(2,2,3):(1,6,2)
raked_product(4:2, 4:1), make_layout_tv(4:2, 4:1)	error	ok

logical_product succeeds on the same inputs (logical_product(4:2, 4:1) = (4,(2,2)):(2,(1,8))); only the pairing step fails.

Changes

• zipped_product: for a single axis, pair the whole block with the whole repetition instead of splitting them with modes(). For one-axis layouts that modes() already split into one entry each, this is the same pair, so inputs that worked before give the same result.
• New test one_axis_products_accept_a_multi_mode_repetition: checks both results above element by element against their definition and that the twelve cells cover offsets 0..12 exactly once.

C++ CuTe's blocked_product accepts this case; its raked_product does not compile for it ("Mismatched Ranks" in detail::zip), so for the raked half this follows the definition and this crate's own logical_product.

Testing

CPU only; the crate has no dependencies, so rustc --edition 2024 --test --crate-name cute_layout src/lib.rs (rustc 1.95.0, aarch64 Linux), main at 44a85d3:

	main	this PR
new test	fails: product: unexpected mode structure	passes
cute-layout unit tests	62 passed, 1 failed	63 passed

rustfmt --check --edition 2024 (1.9.0) is clean on both changed files. A Python port of logical_product and the products, fuzzed against their definition over 3 × 20k cases (with #1712's guard applied), shows 88–121 spurious errors per 20k on main and none with this change.

• just -f cuda-oxide/Justfile check passes (the local mirror of CI: fmt, clippy, tests, guards, docs)
• cargo oxide run <example> passes, or cuda-oxide/scripts/smoketest.sh -o '^<example>$'
• New example added (if applicable)

Checklist

• All commits signed off (git commit -s)
• All commits cryptographically signed and shown as Verified on GitHub (git commit -S)
• SPDX headers on new source files

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