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.

    See Also:
    • "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)