List of periodic functions

This list is incomplete; you can help by . (December 2012)

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.

Trigonometric functions[]

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

U_n is the nth up/down number,

B_n is the nth Bernoulli number

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

Sinus-like functions[]

• Trochoid
• Cycloid
• Clausen function

Non-smooth functions[]

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

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

Vector-valued functions[]

• Epitrochoid
• Epicycloid (special case of the epitrochoid)
• Limaçon (special case of the epitrochoid)
• Hypotrochoid
• Hypocycloid (special case of the hypotrochoid)
• Spirograph (special case of the hypotrochoid)

Doubly periodic functions[]

• Jacobi's elliptic functions
• Weierstrass's elliptic function

Notes[]