O’Riordan, E., M. L. Pickett, and G. I. Shishkin. “Numerical Methods for Singularly Perturbed Elliptic Problems Containing Two Perturbation Parameters”. Mathematical Modelling and Analysis 11, no. 2 (June 30, 2006): 199-212. Accessed December 2, 2024. https://mma.vgtu.lt/index.php/MMA/article/view/9611.