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28.4 Digamma
The digamma function \(\Psi\) is the derivative of the \(\log \Gamma\) function, \[ \Psi(u) \ = \ \frac{d}{d u} \log \Gamma(u) \ = \ \frac{1}{\Gamma(u)} \ \frac{d}{d u} \Gamma(u). \]
The digamma function \(\Psi\) is the derivative of the \(\log \Gamma\) function, \[ \Psi(u) \ = \ \frac{d}{d u} \log \Gamma(u) \ = \ \frac{1}{\Gamma(u)} \ \frac{d}{d u} \Gamma(u). \]