msign Is Wrong for Full-Rank SVD Power Iteration, but Correct for Top-k Subspaces

YouJiacheng · x · 2026-09-18

YouJiacheng revisited an earlier finding: msign used in power iteration is incorrect for SVD, especially in full-rank cases — but he hadn't noticed it is actually correct for top-k subspace estimation.

A useful nuance for implementations of orthogonalization tricks in training methods.

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