/**
* Copyright (C) 2009 - present by OpenGamma Inc. and the OpenGamma group of companies
*
* Please see distribution for license.
*/
package com.opengamma.analytics.math.function.special;
import org.apache.commons.math.special.Gamma;
import com.opengamma.analytics.math.function.Function1D;
/**
*
* The gamma function is a generalization of the factorial to complex and real
* numbers. It is defined by the integral:
* $$
* \begin{equation*}
* \Gamma(z)=\int_0^\infty t^{z-1}e^{-t}dt
* \end{equation*}
* $$
* and is related to the factorial by
* $$
* \begin{equation*}
* \Gamma(n+1)=n!
* \end{equation*}
* $$
* It is analytic everywhere but $z=0, -1, -2, \ldots$
* <p>
* This class is a wrapper for the <a href="http://commons.apache.org/math/api-2.1/org/apache/commons/math/special/Gamma.html">Commons Math library implementation</a>
* of the Gamma function.
*
*/
public class GammaFunction extends Function1D<Double, Double> {
@Override
public Double evaluate(final Double x) {
if (x > 0.0) {
return Math.exp(Gamma.logGamma(x));
}
return Math.PI / Math.sin(Math.PI * x) / evaluate(1 - x);
}
}