The discriminant is a generalization of the　”b ²– 4 ac” formula that everybody knows, which tells us the degeneracy of the (secular) equation. Then it is natural the discriminant is useful for the study of topological phases. Supplemented by the symmetry restriction of the physical non-Hermitian system (electric circuit with registers, for example), the number of exceptional points is discussed within a certain two-dimensional region (section of the three-D as well). Have a look at our recent paper, “Discriminant indicator with generalized rotational symmetry “, by Hiromasa Wakao, Tsuneya Yoshida, and Yasuhiro Hatsugai, which has been published in Phys. Rev. B 105, 214103 (2022) June 1. See also arXiv:2203.05773.