Definition:Digamma Function

Definition

The digamma function, $\psi$, is defined, for $z \in \C \setminus \Z_{\le 0}$, by the logarithmic derivative of the gamma function:

$\map \psi z = \dfrac {\map {\Gamma'} z} {\map \Gamma z}$

where $\Gamma$ is the gamma function, and $\Gamma'$ denotes its derivative.

Also known as

The digamma function is also known as the psi function.

Also see

• Results about the digamma function can be found here.

Sources

• 1989: Ephraim J. Borowski and Jonathan M. Borwein: Dictionary of Mathematics ... (previous) ... (next): digamma function or psi function
• Weisstein, Eric W. "Digamma Function." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/DigammaFunction.html