Finite difference - Wikipedia
https://en.wikipedia.org/wiki/Finite_differenceIn an analogous way, one can obtain finite difference approximations to higher order derivatives and differential operators. For example, by using the above central difference formula for f ′(x + h/2) and f ′(x − h/2) and applying a central difference formula for the derivative of f ′ at x, we obtain the central difference approximation of the second derivative of f: Second-order central
Finite Difference Approximations
web.mit.edu/16.90/BackUp/www/pdfs/Chapter12.pdfFinite difference approximations can also be one-sided. For example, a backward difference approximation is, Uxi ≈ 1 ∆x (Ui −Ui−1)≡δ − x Ui, (97) and a forward difference approximation is, Uxi ≈ 1 ∆x (Ui+1 −Ui)≡δ + x Ui. (98) Exercise 1. Write a MATLAB function which computes the central difference approximation at nodes