C. L. Ejikeme et al. 2021. Discussing a Solution to Nonlinear Duffing Oscillator with Fractional Derivatives Using Homotopy Analysis Method (HAM). Theory and Practice of Mathematics and Computer Science Vol. 6. (Feb. 2021), 57–81. DOI:https://doi.org/10.9734/bpi/tpmcs/v6/3966D.