List_of_periodic_functions Knowpia

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 functionsEdit

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 functionsEdit

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

Vector-valued functionsEdit

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 functionsEdit

NotesEdit

^ Formulae are given as Taylor series or derived from other entries.

^ http://web.mit.edu/jorloff/www/18.03-esg/notes/fourier-tan.pdf^{[bare URL PDF]}
^ Papula, Lothar (2009). Mathematische Formelsammlung: für Ingenieure und Naturwissenschaftler. Vieweg+Teubner Verlag. ISBN 978-3834807571.

[1] Formulae are given as Taylor series or derived from other entries.

[2] ttp://web.mit.edu/jorloff/www/18.03-esg/notes/fourier-tan.pdf^{[bare URL PDF]}

[Papula-3] Papula, Lothar (2009). Mathematische Formelsammlung: für Ingenieure und Naturwissenschaftler. Vieweg+Teubner Verlag. ISBN 978-3834807571.

[nb 1]

[1]

[2]

Summary

Smooth functionsEdit

Non-smooth functionsEdit

Vector-valued functionsEdit

Doubly periodic functionsEdit

NotesEdit