Function special::digamma

pub fn digamma(x: f64) -> f64

Compute the real-valued digamma function.

The digamma function is defined by

       d ln(Γ(x))
ψ(x) = ----------
           dx

where Γ is the Gamma function. The computation is based on an approximation as described in the reference below.

• M. J. Beal, “Variational Algorithms for Approximate Bayesian Inference.” The Gatsby Computational Neuroscience Unit, University College London, 2003, pp. 265–266.

Examples

use special::digamma;

let euler_mascheroni = 0.5772156649015325;
assert_eq!(-euler_mascheroni, digamma(1.0));