Hassan, Abdelgabar Adam, and Shams A. Ahmed. “Apply the Sturm-Liouville Problem With Green’s Function to Linear System”. Communications in Mathematics and Applications 12, no. 3 (September 30, 2021): 699–710. Accessed May 1, 2024. http://www.rgnpublications.com/journals/index.php/cma/article/view/1563.