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In GammaDistributionTest, inlined previous implementation of 

double Gamma.logGamma(doubl)) in order to allow for comparison with new
implementation.
This is in preparation of MATH-849.


git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1378440 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Sebastien Brisard 2012-08-29 04:28:47 +00:00
parent f394970a17
commit 6d0dcae172
1 changed files with 24 additions and 2 deletions
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26
src/test/java/org/apache/commons/math3/distribution/GammaDistributionTest.java
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@ -176,18 +176,40 @@ public class GammaDistributionTest extends RealDistributionAbstractTest {
Assert.assertEquals(dist.getNumericalVariance(), 1.1d * 4.2d * 4.2d, tol);
}
private static final double HALF_LOG_2_PI = 0.5 * FastMath.log(2.0 * FastMath.PI);
public static double logGamma(double x) {
/*
* This is a copy of
* double Gamma.logGamma(double)
* prior to MATH-849
*/
double ret;
if (Double.isNaN(x) || (x <= 0.0)) {
ret = Double.NaN;
} else {
double sum = Gamma.lanczos(x);
double tmp = x + Gamma.LANCZOS_G + .5;
ret = ((x + .5) * FastMath.log(tmp)) - tmp +
HALF_LOG_2_PI + FastMath.log(sum / x);
}
return ret;
}
public static double density(final double x, final double shape,
final double scale) {
/*
* This is a copy of
* double GammaDistribution.density(double)
* prior to r1338548.
* prior to MATH-753.
*/
if (x < 0) {
return 0;
}
return FastMath.pow(x / scale, shape - 1) / scale *
FastMath.exp(-x / scale) / FastMath.exp(Gamma.logGamma(shape));
FastMath.exp(-x / scale) / FastMath.exp(logGamma(shape));
}
/*