time-varying svd

recently i've been trying to see if anyone else has worked on time-varying singular value decompositions. there's surprisingly little out there on it, at least that i can find. i've tried thinking of the svd eigenmodes in terms of rotating coordinate systems. i remembered from dynamics classes once upon a time that some ways of representing rotation have a gimbal lock problem, but quaternions do not. and (i think) they also have linear propagation equations. the wikipedia article on it looks pretty good. i should probably read that and the 'see also' articles at the bottom.