…and easiest of all, Oh, this HIJ, by the way, is a matrix and is called, for peculiar historical reasons, the Hamiltonian matrix. Hamilton worked in 1830, and how he got his name on the quantum mechanical matrix is a tale of history. But it's called the…

…the subject very far, with one possible exception. The most advanced and abstract theory of geometric optics was worked out by Hamilton. And it turns out that this has very important applications in mechanics. But it's even more important in mechanics than…