Rangkuti, Y. M., Side, S., & Noorani, M. S. M. (2014). Numerical Analytic Solution of SIR Model of Dengue Fever Disease in South Sulawesi using Homotopy Perturbation Method and Variational Iteration Method. Journal of Mathematical and Fundamental Sciences, 46(1), 91-105. https://doi.org/10.5614/j.math.fund.sci.2014.46.1.8