Singh, Raghvendra Pratap, and Y. N. Reddy. “Perturbation-Iteration Method for Solving Differential-Difference Equations Having Boundary Layer”. Communications in Mathematics and Applications 11, no. 4 (December 31, 2020): 617–633. Accessed May 3, 2024. http://www.rgnpublications.com/journals/index.php/cma/article/view/1431.