Abd-Elhameed, Waleed M. M. “An Elegant Operational Matrix Based on Harmonic Numbers: Effective Solutions for Linear and Nonlinear Fourth-Order Two Point Boundary Value Problems”. Nonlinear Analysis: Modelling and Control, vol. 21, no. 4, July 2016, pp. 448-64, https://doi.org/10.15388/NA.2016.4.2.