Function special::digamma
[−]
[src]
pub fn digamma(x: f64) -> f64
Compute the real-valued digamma function.
The formula is as follows:
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.
Examples
use special::digamma; const EULER_MASCHERONI: f64 = 0.57721566490153286060651209008240243104215933593992; assert!((digamma(1.0) + EULER_MASCHERONI).abs() < 1e-15);
References
- M. J. Beal, Variational algorithms for approximate Bayesian inference. University of London, 2003, pp. 265–266.