SuanShu, a Java numerical and statistical library

com.numericalmethod.suanshu.analysis.function.special.gamma

Class Digamma

• All Implemented Interfaces:
Function<Vector,Double>, RealScalarFunction, UnivariateRealFunction

public class Digamma
extends AbstractUnivariateRealFunction
The digamma function is defined as the logarithmic derivative of the gamma function. That is, $\psi(x) =\frac{d}{dx} \ln{\Gamma(x)}= \frac{\Gamma'(x)}{\Gamma(x)}$

This implementation is based on Algorithm 610.

• "D. E. Amos, "Algorithm 610: A Portable FORTRAN Subroutine for Derivatives of the Psi Function," ACM Transactions on Mathematical Software (TOMS), Volume 9, Issue 4 (December 1983), p. 494 - 502."
• "Shanjie Zhang, Jianming Jin, Computation of Special Functions. Wiley-Interscience; Har/Dis edition (July 12, 1996)."
• Wikipedia: Digamma function
• Constructor Detail

• Digamma

public Digamma()
• Method Detail

• evaluate

public double evaluate(double x)
Description copied from interface: UnivariateRealFunction
Evaluate y = f(x).
Parameters:
x - x
Returns:
f(x)