Kazanko, O.V., Penkina, O.E. and Golovko, O.V. 2025. Development of a methodology for transitioning from a spectral equation relative to a spatial variable to a differential equation relative to a spectral parameter in the Sturm-Liouville problem for a one-dimensional periodic two-layer photonic crystal. Visnyk of V.N. Karazin Kharkiv National University, series “Radio Physics and Electronics”. 42 (Jul. 2025), 55-63. DOI:https://doi.org/10.26565/2311-0872-2025-42-06.