Tao, Zhao-Ling. “Frequency-Amplitude Relationship of the Duffing-Harmonic Oscillator”. Topological Methods in Nonlinear Analysis 31, no. 2 (June 1, 2008): 279–285. Accessed July 22, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2008.019.