Logarithmic chart of a matrix Lie group (source code)

= Logarithmic chart of a matrix Lie group

For a matrix Lie group $G$ with Lie algebra $\mathfrak g=T_I G$, choose neighborhoods on which $\exp:\mathfrak g\to G$ and $\log:G\to\mathfrak g$ are inverse. Left translation gives a chart near $g\in G$ by
$$
h\longmapsto\log(g^{-1}h).
$$
The <Baker--Campbell--Hausdorff formula> expresses multiplication smoothly in these coordinates.