Digamma
From specialfunctionswiki
The digamma function $\psi$ is defined by $$\psi(z) = \dfrac{d}{dz} \log \Gamma(z) = \dfrac{\Gamma'(z)}{\Gamma(z)}.$$
The digamma function $\psi$ is defined by $$\psi(z) = \dfrac{d}{dz} \log \Gamma(z) = \dfrac{\Gamma'(z)}{\Gamma(z)}.$$
