7.27 Psi (Digamma) Function

The polygamma functions of order m 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'.

7.27.1 Digamma Function
7.27.2 Trigamma Function
7.27.3 Polygamma Function