Nikitin, A. G., and R. O. Popovich. “Group Classification of Nonlinear Schrödinger Equations”. Ukrains’kyi Matematychnyi Zhurnal 53, no. 8 (August 25, 2001): 1053-1060. Accessed May 19, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4326.