 Digamma function

The digamma function is the logarithmic derivativeLogarithmically differentiating the Weierstrass product gives

The digamma function, denoted as \( \psi(x) \), is the logarithmic derivative of the gamma function \( \Gamma(x) \). Mathematically, it is defined as: \[ \psi(x) = \frac{d}{dx} \ln(\Gamma(x)) = \frac{\Gamma'(x)}{\Gamma(x)} \] where \( \Gamma'(x) \) is the derivative of the gamma function.