7.27 Psi (Digamma) Function

The polygamma functions of order m are defined by

     \psi^{(m)}(x) = (d/dx)^m \psi(x) = (d/dx)^{m+1} \log(\Gamma(x))

where \psi(x) = \Gamma'(x)/\Gamma(x) is known as the digamma function. These functions are declared in the header file gsl_sf_psi.h.

• Digamma Function
• Trigamma Function
• Polygamma Function