Wright omega function

In mathematics, the Wright omega function or Wright function,^{[note 1]} denoted ω, is defined in terms of the Lambert W function as:

${\displaystyle \omega (z)=W_{{\big \lceil }{\frac {\mathrm {Im} (z)-\pi }{2\pi }}{\big \rceil }}(e^{z}).}${\displaystyle \omega (z)=W_{{\big \lceil }{\frac {\mathrm {Im} (z)-\pi }{2\pi }}{\big \rceil }}(e^{z}).}

It is simpler to be defined by its inverse function

${\displaystyle z(\omega )=\ln(\omega )+\omega }${\displaystyle z(\omega )=\ln(\omega )+\omega }

One of the main applications of this function is in the resolution of the equation z = ln(z), as the only solution is given by z = e^−ω(π i).

y = ω(z) is the unique solution, when ${\displaystyle z\neq x\pm i\pi }${\displaystyle z\neq x\pm i\pi } for x ≤ −1, of the equation y + ln(y) = z. Except for those two values, the Wright omega function is continuous, even analytic.

The Wright omega function satisfies the relation ${\displaystyle W_{k}(z)=\omega (\ln(z)+2\pi ik)}${\displaystyle W_{k}(z)=\omega (\ln(z)+2\pi ik)}.

It also satisfies the differential equation

${\displaystyle {\frac {d\omega }{dz}}={\frac {\omega }{1+\omega }}}${\displaystyle {\frac {d\omega }{dz}}={\frac {\omega }{1+\omega }}}

wherever ω is analytic (as can be seen by performing separation of variables and recovering the equation ${\displaystyle \ln(\omega )+\omega =z}${\displaystyle \ln(\omega )+\omega =z}, and as a consequence its integral can be expressed as:

${\displaystyle \int \omega ^{n},円dz={\begin{cases}{\frac {\omega ^{n+1}-1}{n+1}}+{\frac {\omega ^{n}}{n}}&{\mbox{if }}n\neq -1,\\\ln(\omega )-{\frac {1}{\omega }}&{\mbox{if }}n=-1.\end{cases}}}${\displaystyle \int \omega ^{n},円dz={\begin{cases}{\frac {\omega ^{n+1}-1}{n+1}}+{\frac {\omega ^{n}}{n}}&{\mbox{if }}n\neq -1,\\\ln(\omega )-{\frac {1}{\omega }}&{\mbox{if }}n=-1.\end{cases}}}

Its Taylor series around the point ${\displaystyle a=\omega _{a}+\ln(\omega _{a})}${\displaystyle a=\omega _{a}+\ln(\omega _{a})} takes the form :

${\displaystyle \omega (z)=\sum _{n=0}^{+\infty }{\frac {q_{n}(\omega _{a})}{(1+\omega _{a})^{2n-1}}}{\frac {(z-a)^{n}}{n!}}}${\displaystyle \omega (z)=\sum _{n=0}^{+\infty }{\frac {q_{n}(\omega _{a})}{(1+\omega _{a})^{2n-1}}}{\frac {(z-a)^{n}}{n!}}}

where

${\displaystyle q_{n}(w)=\sum _{k=0}^{n-1}{\bigg \langle }\!\!{\bigg \langle }{\begin{matrix}n+1\\k\end{matrix}}{\bigg \rangle }\!\!{\bigg \rangle }(-1)^{k}w^{k+1}}${\displaystyle q_{n}(w)=\sum _{k=0}^{n-1}{\bigg \langle }\!\!{\bigg \langle }{\begin{matrix}n+1\\k\end{matrix}}{\bigg \rangle }\!\!{\bigg \rangle }(-1)^{k}w^{k+1}}

in which

${\displaystyle {\bigg \langle }\!\!{\bigg \langle }{\begin{matrix}n\\k\end{matrix}}{\bigg \rangle }\!\!{\bigg \rangle }}${\displaystyle {\bigg \langle }\!\!{\bigg \langle }{\begin{matrix}n\\k\end{matrix}}{\bigg \rangle }\!\!{\bigg \rangle }}

is a second-order Eulerian number.

${\displaystyle {\begin{array}{lll}\omega (0)&=W_{0}(1)&\approx 0.56714\\\omega (1)&=1&\\\omega (-1\pm i\pi )&=-1&\\\omega (-{\frac {1}{3}}+\ln \left({\frac {1}{3}}\right)+i\pi )&=-{\frac {1}{3}}&\\\omega (-{\frac {1}{3}}+\ln \left({\frac {1}{3}}\right)-i\pi )&=W_{-1}\left(-{\frac {1}{3}}e^{-{\frac {1}{3}}}\right)&\approx -2.237147028\\\end{array}}}${\displaystyle {\begin{array}{lll}\omega (0)&=W_{0}(1)&\approx 0.56714\\\omega (1)&=1&\\\omega (-1\pm i\pi )&=-1&\\\omega (-{\frac {1}{3}}+\ln \left({\frac {1}{3}}\right)+i\pi )&=-{\frac {1}{3}}&\\\omega (-{\frac {1}{3}}+\ln \left({\frac {1}{3}}\right)-i\pi )&=W_{-1}\left(-{\frac {1}{3}}e^{-{\frac {1}{3}}}\right)&\approx -2.237147028\\\end{array}}}

• Plots of the Wright omega function on the complex plane
• '"`UNIQ--postMath-0000000D-QINU`"'
  ${\displaystyle z=\Re \{\omega (x+iy)\}}${\displaystyle z=\Re \{\omega (x+iy)\}}
• '"`UNIQ--postMath-0000000E-QINU`"'[note 2]
  ${\displaystyle z=\Im \{\omega (x+iy)\}}${\displaystyle z=\Im \{\omega (x+iy)\}}^{[note 2]}
• '"`UNIQ--postMath-0000000F-QINU`"'
  ${\displaystyle z=|\omega (x+iy)|}${\displaystyle z=|\omega (x+iy)|}

• "The Wright ω function", Robert Corless and David Jeffrey

• Special functions

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• Use American English from March 2019
• All Wikipedia articles written in American English
• Accuracy disputes from August 2025
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