We validate Fisher Information Matrix rank as an exact, parameter-free measure of effective spatial dimension. Key results: exact integer dimension on flat tori through d=4, Hausdorff dimension on fractals, a novel disorder direction on random geometric graphs. Code available at github. com/IanD25/Dₑff-Test-1. 0. Preprint pending arXiv endorsement
Ian Darling (Sun,) studied this question.