The equation shown is a type of decomposition of a Lie algebra g that was introduced by Élie Cartan in his doctoral thesis. h is called a Cartan subalgebra of g.
To answer what a Lie algebra is, an extremely hand-wavy description might be: a Lie group is a continuous group of symmetries of some geometric object (for example, the group SO(3) of rotations of three-dimensional space), and the corresponding Lie algebra is the “tangent space” to the group, that is, the space of tiny changes you can make that lie “along” the group.
A lot of things in Lie theory and differential geometry are named after Élie Cartan, or sometimes after his son Henri.
Phoenix3875@lemmy.world 3 weeks ago
It’s more of a math meme: Cartan Subalgebra.
Cattypat@lemmy.blahaj.zone 3 weeks ago
lmao I went down a whole rabbit hole with the links in this page and I do not understand ANYTHING here. math is not my thing
iAvicenna@lemmy.world 3 weeks ago
I see gothic small letters my brain goes LIE!