MinenkoA. S. “On Minimization of One Integral Functional by the Ritz Method”. Ukrains’kyi Matematychnyi Zhurnal 58, no. 10 (October 25, 2006): 1385–1394. Accessed November 22, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3540.