- Any function whoever worth repeats following the regular inclusion of a period to its independent variable; i.e. f(x+t) = f(x) for a few t overall x
- a function whose values recur at fixed intervals as the adjustable uniformly increases. The trigonomertic functions, as sin x, tan x, etc., tend to be periodic functions. Exponential features are periodic, having an imaginary duration, and also the elliptic features haven't only a real but an imaginary period, as they are therefore known as doubly periodic.