Arnold's Cat (2018)
(gerdbreitenbach.de)31 points by bradly 7 days ago
31 points by bradly 7 days ago
One can still define a map by taking the fractional part of the matrix-vector product, but the resulting map won't be continuous (with respect to the topology of the torus). In addition, if one wants the map be a homeomorphism (continuous with continuous inverse) then the determinant must have absolute value 1.
I clicked the link wondering if it would be about this "Arnold the Cat" or perhaps related to Simon's Cat:
The page doesn't say why matrices need to have whole-number (really just integer) entries, but I'd suspect it's because bad approximations to non-integer rationals accumulate sufficiently to make the recurrence unrecognizable.