Luo, Albert C.J., and Bo Yu. “Period-M Motions and Bifurcation Trees in a Periodically Excited, Quadratic Nonlinear Oscillator”. Discontinuity, Nonlinearity, and Complexity, vol. 2, no. 3, Aug. 2026, pp. 263-88, https://doi.org/10.5890/DNC.2013.08.004.