A Nonstandard Fitted Operator Method for Singularly Perturbed Parabolic Reaction-Diffusion Problems with a Large Time Delay

In this paper, we design and investigate a higher order ? -uniformly convergent method to solve singularly perturbed parabolic reaction-diffusion problems with large time delay. We use the Crank–Nicolson for derivative, while spatial derivative is discretized using nonstandard finite difference approach on uniform mesh. Furthermore, improve of convergence, used Richardson extrapolation technique. The designed scheme converges independent perturbation parameter ( id="M2"> convergent) also achieves fourth-order in both variables. Two model examples are considered demonstrate applicability suggested method. proposed produces better accuracy rate convergence than some methods that appear literature.