Finite difference - Wikipedia
https://en.wikipedia.org/wiki/Finite_differenceThree basic types are commonly considered: forward, backward, and central finite differences. A forward difference, denoted [], of a function f is a function defined as [] = (+) ().Depending on the application, the spacing h may be variable or constant. When omitted, h is taken to be 1; that is, [] = [] = (+) ().A backward difference uses the function values at x and x − h, instead of the ...