2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/57868The paper presents a new theory of unfolding of eigenvalue surfaces of real symmetric and Hermitian matrices due to an arbitrary complex perturbation near a diabolic point. General asymptotic formulae describing deformations of a conical surface for different kinds of perturbing matrices are derived. As a physical application, singularities of the surfaces of refractive indices in crystal optics are studied.23 pages, 7 figuresMathematical Physicstext