ZHANG, Ruda March 03, 2021:  Use mathcal for big O notation, to distinguish from the orthogonal group. [69caae9]
ZHANG, Ruda June 17, 2020:  Formatting. More on manifolds: integral manifold, distribution, foliation; covariant derivative along curve in submanifold; higher-order retraction. [c08c622]
ZHANG, Ruda June 05, 2020:  More on manifolds: curvature concepts; bounds for sectional and Ricci curvature. [0b35b68]
ZHANG, Ruda May 28, 2020:  More on manifold: geodesic, higher-order retraction, matrix manifolds, horizontal lift, C^k regular level set theorem, zero section, curvature. [22084b8]
ZHANG, Ruda May 28, 2020:  Add optimization on manifold. [f036f0e]