Finite difference - Wikipedia
https://en.wikipedia.org/wiki/Finite_differenceThe forward difference can be considered as an operator, called the difference operator, which maps the function f to Δh[ f ]. This operator amounts to where Th is the shift operator with step h, defined by Th[ f ](x) = f (x + h), and I is the identity operator. The finite difference of higher orders can be defined in recursive manner as Δ h ≡ Δh(Δ h). Anoth…