nondiagonal element
1Coxeter group — In mathematics, a Coxeter group, named after H.S.M. Coxeter, is an abstract group that admits a formal description in terms of mirror symmetries. Indeed, the finite Coxeter groups are precisely the finite Euclidean reflection groups; the symmetry …
2Ritz method — In physics, the Ritz method is a variational method named after Walter Ritz.In quantum mechanics, a system of particles can be described in terms of an energy functional or Hamiltonian, which will measure the energy of any proposed configuration… …
