In mathematics, a difference operator maps a function, f(x), to another function, f(x + a) − f(x + b).
The forward difference operator
\Delta f(x)=f(x+1)-f(x)
occurs frequently in the calculus of finite differences, where it plays a role formally similar to that of the derivative, but used in discrete circumstances. Difference equations can often be solved with techniques very similar to those for solving differential equations. Analogously we can have the backward difference operator
\nabla f(x)=f(x)-f(x-1)
When restricted to polynomial functions f, the forward difference operator is a delta operator, i.e., a shift-equivariant linear operator on polynomials that reduces degree by 1.