HE, Ji-Huan. Nonlinear Mathieu Equation and its Approximation Without a Small Parameter. Engineering Transactions, [S. l.], v. 50, n. 1-2, p. 43–54, 2015. DOI: 10.24423/engtrans.507.2002. Disponível em: https://et.ippt.pan.pl/index.php/et/article/view/507. Acesso em: 22 jul. 2025.