A function is said to be periodic (or, when emphasizing the presence of a single period instead of multiple periods, singly periodic) with period if
f(x)=f(x+np)
where n=1,2.........
p is the Fundamental Period
The constant function is periodic with any period for all nonzero real numbers , so there is no concept analogous to the least period for constant functions.
An aperiodic function never repeats, although technically an aperiodic function can be considered like a periodic function with an infinite period.
f(x+p)=-f(x)
