Klibanov, M., and A. Timonov. “A Globally Convergent Convexification Algorithm for the Inverse Problem of Electromagnetic Frequency Sounding in One Dimension”. Numerical Methods and Programming (Vychislitel’nye Metody I Programmirovanie), vol. 4, no. 4, Feb. 2003, pp. 52-81, https://en.num-meth.ru/index.php/journal/article/view/76.