List of periodic functions

This is a list of some well-known periodic functions. The constant function $f (x) = c$ , where $c$ is independent of $x$ , is periodic with any period, but lacks a fundamental period. A definition is given for some of the following functions, though each function may have many equivalent definitions.

Smooth functions

All trigonometric functions listed have period $2\pi$ , unless otherwise stated. For the following trigonometric functions:

U n

is the

n

th up/down number,

B n

is the

n

th Bernoulli number

Name	Symbol	Formula ^{[nb 1]}	Fourier Series
Sine	$\sin(x)$	$\sum _{n=0}^{\infty }{\frac {(-1)^{n}x^{2n+1}}{(2n+1)!}}$	$\sin(x)$
cas (mathematics)	$\operatorname {cas} (x)$	$\sin(x)+\cos(x)$	$\sin(x)+\cos(x)$
Cosine	$\cos(x)$	$\sum _{n=0}^{\infty }{\frac {(-1)^{n}x^{2n}}{(2n)!}}$	$\cos(x)$
cis (mathematics)	$e^{ix},\operatorname {cis} (x)$	$cos(x) + i sin(x)$	$\cos(x)+i\sin(x)$
Tangent	$\tan(x)$	$\sum _{n=0}^{\infty }{\frac {U_{2n+1}x^{2n+1}}{(2n+1)!}}$	$2\sum _{n=1}^{\infty }(-1)^{n-1}\sin(2nx)$ ^[1]
Cotangent	$\cot(x)$	$\sum _{n=0}^{\infty }{\frac {(-1)^{n}2^{2n}B_{2n}x^{2n-1}}{(2n)!}}$	$i+2i\sum _{n=1}^{\infty }(\cos 2nx-i\sin 2nx)$ ^{[citation needed]}
Secant	$\sec(x)$	$\sum _{n=0}^{\infty }{\frac {U_{2n}x^{2n}}{(2n)!}}$	-
Cosecant	$\csc(x)$	$\sum _{n=0}^{\infty }{\frac {(-1)^{n+1}2\left(2^{2n-1}-1\right)B_{2n}x^{2n-1}}{(2n)!}}$	-
Exsecant	$\operatorname {exsec} (x)$	$\sec(x)-1$	-
Excosecant	$\operatorname {excsc} (x)$	$\csc(x)-1$	-
Versine	$\operatorname {versin} (x)$	$1-\cos(x)$	$1-\cos(x)$
Vercosine	$\operatorname {vercosin} (x)$	$1+\cos(x)$	$1+\cos(x)$
Coversine	$\operatorname {coversin} (x)$	$1-\sin(x)$	$1-\sin(x)$
Covercosine	$\operatorname {covercosin} (x)$	$1+\sin(x)$	$1+\sin(x)$
Haversine	$\operatorname {haversin} (x)$	${\frac {1-\cos(x)}{2}}$	${\frac {1}{2}}-{\frac {1}{2}}\cos(x)$
Havercosine	$\operatorname {havercosin} (x)$	${\frac {1+\cos(x)}{2}}$	${\frac {1}{2}}+{\frac {1}{2}}\cos(x)$
Hacoversine	$\operatorname {hacoversin} (x)$	${\frac {1-\sin(x)}{2}}$	${\frac {1}{2}}-{\frac {1}{2}}\sin(x)$
Hacovercosine	$\operatorname {hacovercosin} (x)$	${\frac {1+\sin(x)}{2}}$	${\frac {1}{2}}+{\frac {1}{2}}\sin(x)$
Magnitude of sine wave with amplitude, A, and period, T	-	$A\|\sin \left({\frac {2\pi }{T}}x\right)\|$	${\frac {4A}{2\pi }}+\sum _{n\,\mathrm {even} }{\frac {-4A}{\pi }}{\frac {1}{1-n^{2}}}\cos({\frac {2\pi n}{T}}x)$ ^[2]^{: p. 193}
Clausen function	$\operatorname {Cl} _{2}(x)$	$-\int _{0}^{x}\ln \left\|2\sin {\frac {x}{2}}\right\|dx$	$\sum _{k=1}^{\infty }{\frac {\sin kx}{k^{2}}}$

Non-smooth functions

The following functions have period $p$ and take $x$ as their argument. The symbol $\lfloor n\rfloor$ is the floor function of $n$ and $\operatorname {sgn}$ is the sign function.

Name	Formula	Fourier Series	Notes
Triangle wave	${\frac {4}{p}}\left(x-{\frac {p}{2}}\left\lfloor {\frac {2x}{p}}+{\frac {1}{2}}\right\rfloor \right)(-1)^{\left\lfloor {\frac {2x}{p}}+{\frac {1}{2}}\right\rfloor }$	${\frac {8}{\pi ^{2}}}\sum _{n\,\mathrm {odd} }^{\infty }{\frac {(-1)^{(n-1)/2}}{n^{2}}}\sin \left({\frac {2\pi nx}{p}}\right)$	non-continuous first derivative
Sawtooth wave	$2\left({\frac {x}{p}}-\left\lfloor {\frac {1}{2}}+{\frac {x}{p}}\right\rfloor \right)$	${\frac {2}{\pi }}\sum _{n=1}^{\infty }{\frac {(-1)^{n-1}}{n}}\sin \left({\frac {2\pi nx}{p}}\right)$	non-continuous
Square wave	$\operatorname {sgn} \left(\sin {\frac {2\pi x}{p}}\right)$	${\frac {4}{\pi }}\sum _{n\,\mathrm {odd} }^{\infty }{\frac {1}{n}}\sin \left({\frac {2\pi nx}{p}}\right)$	non-continuous
Cycloid	${\frac {p-p\cos \left(f^{(-1)}\left({\frac {2\pi x}{p}}\right)\right)}{2\pi }}$ given $f(x)=x-\sin(x)$ and $f^{(-1)}(x)$ is its real-valued inverse.	${\frac {p}{\pi }}{\biggl (}{\frac {3}{4}}+\sum _{n=1}^{\infty }{\frac {\operatorname {J} _{n}(n)-\operatorname {J} _{n-1}(n)}{n}}\cos {\Bigl (}{\frac {2\pi nx}{p}}{\Bigr )}{\biggr )}$ where $\operatorname {J} _{n}(x)$ is the Bessel Function of the first kind.	non-continuous first derivative
Pulse wave	$H\left(\cos \left({\frac {2\pi x}{p}}\right)-\cos \left({\frac {\pi t}{p}}\right)\right)$ where $H$ is the Heaviside step function t is how long the pulse stays at 1	${\frac {t}{p}}+\sum _{n=1}^{\infty }{\frac {2}{n\pi }}\sin \left({\frac {\pi nt}{p}}\right)\cos \left({\frac {2\pi nx}{p}}\right)$	non-continuous
Dirichlet function	${\displaystyle \mathbf {1} _{\mathbb {Q} }(x)={\begin{cases}1&x\in \mathbb {Q} \\0&x\notin \mathbb {Q} \end{cases}}}$	-	non-continuous