Distances and Riemannian metrics for multivariate spectral densities
  We first introduce a class of divergence measures between power spectral density matrices. These are derived by comparing the suitability of different models in the context of optimal prediction. Distances between "infinitesimally close" power spectra are quadratic, and hence, they induce a differential-geometric structure. We study the corresponding Riemannian metrics and, for a particular case, provide explicit formulae for the corresponding geodesics and geodesic distances. The close connection between the geometry of power spectra and the geometry of the Fisher-Rao metric is noted. 
Xianhua Jiang, Lipeng Ning, and Tryphon T. Georgiou
math.OC cs.SY math.ST stat.TH