com.numericalmethod.suanshu.analysis.function.special
Class Digamma

java.lang.Object
  com.numericalmethod.suanshu.analysis.function.rn2r1.UnivariateRealFunction
      com.numericalmethod.suanshu.analysis.function.special.Digamma

All Implemented Interfaces:

Function, RealScalarFunction

public class Digamma
extends UnivariateRealFunction

The digamma function is defined as the logarithmic derivative of the gamma function.

         d               Γ'(x)
 ψ(x) = ----log(Γ(x)) = -------
         dx              Γ(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

Nested Class Summary

Nested classes/interfaces inherited from interface com.numericalmethod.suanshu.analysis.function.Function

Function.EvaluationException

Constructor Summary

Digamma()

Method Summary

double

evaluate(double x) Compute f(x).

Methods inherited from class com.numericalmethod.suanshu.analysis.function.rn2r1.UnivariateRealFunction

dimension4Domain, dimension4Range, evaluate

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Digamma

public Digamma()

Method Detail

evaluate

public double evaluate(double x)

Description copied from class: UnivariateRealFunction

Compute f(x).

Specified by:

evaluate in class UnivariateRealFunction

Parameters:

x - x

Returns:

f(x)