https://github.com/adrianjav/pogo — POGO: A Proximal One-step Geometric Orthoptimizer
https://arxiv.org/abs/2602.14656 — An Embarrassingly Simple Way to Optimize Orthogonal Matrices at Scale; Adrián Javaloy, Antonio Vergari
I wonder what would be the result if they used a matrix that is orthogonal and closest to the source matrix. Usually one uses the Frobenius norm (root of the sum of all squared matrix entries). Maybe, one could even try another norm that gives a sparser matrix.