Vakhitov–Kolokolov
The Vakhitov–Kolokolov stability criterion is a condition for linear stability (sometimes called spectral stability) ofsolitary wave solutions to a wide class of U(1)-invariant Hamiltonian systems, named after Russian scientists Aleksandr Kolokolov (Александр Александрович Колоколов) and Nazib Vakhitov (Назиб Галиевич Вахитов).