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https://issues.apache.org/jira/browse/MATH-294?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Phil Steitz closed MATH-294.
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> RandomDataImpl.nextPoisson fails for means in range 6.0 - 19.99
> ---------------------------------------------------------------
>
> Key: MATH-294
> URL: https://issues.apache.org/jira/browse/MATH-294
> Project: Commons Math
> Issue Type: Bug
> Affects Versions: 1.2, 2.0
> Environment: Java 1.6 on mac osX
> Reporter: Jason McFall
> Fix For: 2.1
>
> Attachments: math-294.patch
>
>
> math.random.RandomDataImpl.nextPoisson(double mean) fails frequently (but not
> always) for values of mean between 6.0 and 19.99 inclusive. For values below
> 6.0 (where I see there is a branch in the logic) and above 20.0 it seems to
> be okay (though I've only randomly sampled the space and run a million trials
> for the values I've tried)
> When it fails, the exception is as follows (this for a mean of 6.0)
> org.apache.commons.math.MathRuntimeException$4: must have n >= 0 for n!, got
> n = -2
> at
> org.apache.commons.math.MathRuntimeException.createIllegalArgumentException(MathRuntimeException.java:282)
> at
> org.apache.commons.math.util.MathUtils.factorialLog(MathUtils.java:561)
> at
> org.apache.commons.math.random.RandomDataImpl.nextPoisson(RandomDataImpl.java:434)
>
> ie MathUtils.factorialLog is being called with a negative input
> To reproduce:
> JDKRandomGenerator random = new JDKRandomGenerator();
> random.setSeed(123456);
> RandomData randomData = new RandomDataImpl(random);
> for (int i=0; i< 1000000; i++){
> randomData.nextPoisson(6.0);
> }
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