As widely accepted, the degeneracy of eigenvalues of the Hamiltonian is a singular point, which is the source of the non-trivial topology. Then it is more than natural that the discriminant of the secular equation is useful to define a topological invariant of the physical system. Note that the discriminant is obtained without diagonalization (remember “b2-4 a c” formula for an order 2 case). Here it is used for a non-Hermitian problem with some symmetry protection. Look at our recent paper, “Discriminant indicators with generalized inversion symmetry” by Tsuneya Yoshida, Ryo Okugawa, and Yasuhiro Hatsugai, Phys. Rev. B 105, 085109 (2022) published on 7 February 2022. It is also accessible by arXiv:2111.07077.