Ladeveze, P., L. . Arnaud, P. . Rouch, and C. . Blanze. “La Theorie Variationnelle Des Rayons Complexes Pour Le Calcul Des Vibrations Moyennes Frequences”. European Journal of Computational Mechanics, vol. 9, no. 1-3, Mar. 2000, pp. 67-88, https://journals.riverpublishers.com/index.php/EJCM/article/view/2929.