Cakir, Z., and A. Sendur. “A Note on Epidemiologic Models: SIR Modeling of the COVID-19 With Variable Coefficients”. Bulletin of the Karaganda University. Mathematics Series 105, no. 1 (March 30, 2022): 43–51. Accessed July 3, 2025. https://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/464.