[STATISTICS-23] Parameter names in "GammaDistribution"

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Fix Version/s: 1.0
• Component/s: distribution
• Assignee: Gilles Sadowski
• Reporter: Gilles Sadowski
• Created: 12/Apr/20 11:17
• Updated: 06/Dec/22 11:30
• Resolved: 12/Apr/20 11:27

Description

After upgrading to v1.3 of "Commons RNG", a unit test for GammaDistribution fails:

[ERROR]   GammaDistributionTest>ContinuousDistributionAbstractTest.testSampler:342 Chisquare test failed p-value = 1.1102230246251565E-15 chisquare statistic = 72.63199999999999. 
value   expected        observed
1       250             355
2       250             183
3       250             200
4       250             262

It is caused by the inversion of the parameters when instantiating the sampler (at line ):

    public ContinuousDistribution.Sampler createSampler(final UniformRandomProvider rng) {
        // Gamma distribution sampler.
        return new AhrensDieterMarsagliaTsangGammaSampler(rng, scale, shape)::sample;
    }

Things are back to normal when switching the scale and shape arguments.

Issue Links

• is caused by: RNG-96 AhrensDieterMarsagliaTsangGammaSampler incorrectly names parameters