Gadylshin, K.G., and M.I. Protasov. “Calculation of Exact Frequency-Dependent Rays When the Solution of the Helmholtz Equation Is Known”. Numerical Methods and Programming (Vychislitel’nye Metody i Programmirovanie) 16, no. 46 (October 14, 2015): 586–594. Accessed April 25, 2024. https://en.num-meth.ru/index.php/journal/article/view/861.