Fitted tension spline method for singularly perturbed parabolic problem with a large temporal lag

We develop a fitted tension spline numerical scheme for singularly per-turbed parabolic problems with a large temporal lag. A priori bounds and properties of the continuous solution are discussed. Due to the problem’s small parameter ε, as a multiple diffusion term, the solution possesses a multi-scale character in the boundary layer region, which is exhibited on the right side of the domain. This results in a challenging duty to solve such problems analytically or using classical numerical methods. Classi-cal numerical methods cause spurious nonphysical oscillations unless an unacceptable number of mesh points is considered, which requires a high computational cost. To handle this difficulty, the method comprises the Crank–Nicolson method in the temporal direction and the fitted spline method in the spatial direction on uniform meshes. The stability of the method is studied using the discrete maximum principle and discrete solu-tion bounds. We proved that the proposed scheme is uniformly convergent, with an order one in the space and an order two in the time directions. Two numerical examples are considered to validate the efficiency and applica-bility of the proposed scheme. Furthermore, the boundary layer behavior of the solutions is given graphically.