# 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:

$\displaystyle \psi \left({z}\right) = \frac {\Gamma' \left({z}\right)} {\Gamma\left({z}\right)}$

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

## Also see

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