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 Details

    • Digamma

      public Digamma()
  • Method Details

    • evaluate

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