... Gen. 38 (2005) 5531­5546 doi:10.1088/0305-4470/38/24/007 Unfolding of eigenvalue surfaces near a diabolic point due to a complex perturbation O N Kirillov, A A Mailybaev and A P Seyranian Institute of Mechanics, Moscow State Lomonosov University, Michurinskii pr. ... In the case of real symmetric matrices we study the unfolding of eigenvalue surfaces near a diabolic point under real and complex perturbations. ... A real non-symmetric perturbation of a diabolic point. c 0: Im2 + (x + )2 + (y + )2 = 2...