ZHANG, Ruda September 08, 2021:  More on Bonnabel2010. [16f7aeb]
ZHANG, Ruda March 28, 2021:  More on product manifold; fix typo. [06eeb18]
ZHANG, Ruda March 09, 2021:  Defind mode, median; more on Gaussian rv, probabilistic models on matrix manifolds. [7c5a23c]
ZHANG, Ruda March 07, 2021:  More on probabilistic models on matrix manifolds. [97edf7f]
ZHANG, Ruda March 03, 2021:  More on probabilistic models on manifolds and matrix manifolds, matrix-variate functions, matrix functions. [92128e2]
ZHANG, Ruda March 03, 2021:  Use mathcal for big O notation, to distinguish from the orthogonal group. [69caae9]
ZHANG, Ruda March 03, 2021:  Add probabilistic models on matrix manifolds. [553ad3f]