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https://issues.apache.org/jira/browse/MATH-1384?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15466579#comment-15466579
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Gilles commented on MATH-1384:
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This seems to be the same issue as MATH-1356.
> HypergeometricDistribution logProbability() returns NaN for edge cases
> ----------------------------------------------------------------------
>
> Key: MATH-1384
> URL: https://issues.apache.org/jira/browse/MATH-1384
> Project: Commons Math
> Issue Type: Bug
> Affects Versions: 3.0, 4.0
> Reporter: Arman Bilge
> Priority: Minor
>
> For certain edge cases, HypergeometricDistribution.logProbability() will
> return NaN.
> To compute the hypergeometric log probability, three binomial log
> probabilities are computed and then combined accordingly. The implementation
> is essentially the same as in BinomialDistribution.logProbability() and uses
> the SaddlePointExpansion. However, the Binomial implementation includes an
> extra check for the edge case of 0 trials which the HyperGeometric lacks.
> An example call which fails is:
> new HypergeometricDistribution(null, 11, 0, 1).logProbability(0)
> which returns NaN instead of 0.0.
> Note that
> new HypergeometricDistribution(null, 10, 0, 1).logProbability(0)
> returns 0 as expected.
> Possible fixes:
> 1. Check for the edge cases and return appropriate values. This would make
> the code somewhat more complex.
> 2. Instead of duplicating the implementation use
> BinomialDistribution.logProbability(). This is much simpler/more readable but
> will reduce performance as each call to BinomialDistribution.logProbability()
> makes redundant checks of validity of input parameters etc.
> I am happy to submit a PR at the GitHub repo implementing either 1 or 2 with
> the necessary tests.
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