A. S. Minenko, “On minimization of one integral functional by the Ritz method”, Ukr. Mat. Zhurn., vol. 58, no. 10, pp. 1385–1394, Oct. 2006, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3540