Re: [bug report] Commons-Math binomial distribution method returns 1 when it should return 0

[Al Chou <Ho...@Yahoo.com>]

As Brent says in the latest comment on the bug report, the cumulative 
probability does seem to be behaving as its mathematical definition 
specifies.  Perhaps what is wanted by the reporter is not just the 
cumulative probability at a point n but rather the difference between 
the cumulative probabilities at two points surrounding n, e.g, 
cumulativeProbability(n + 1) - cumulativeProbability(n - 1) for the 
discrete case (or x + dx and x - dx for the continuous case).

Al



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>http://issues.apache.org/bugzilla/show_bug.cgi?id=28829
>
>[bug report] Commons-Math binomial distribution method returns 1 
>when it should return 0
>
>            Summary: [bug report] Commons-Math binomial distribution method
>                     returns 1 when it should return 0
>            Product: Commons
>            Version: unspecified
>           Platform: All
>                URL: http://http://
>         OS/Version: All
>             Status: NEW
>           Severity: Normal
>           Priority: Other
>          Component: Math
>         AssignedTo: commons-dev@jakarta.apache.org
>         ReportedBy: mdiggory@latte.harvard.edu
>
>
>I wanted to open a ticket for this issue so we can address it formally.
>
>-Mark.
>
>-------- Original Message --------
>
>Dear Mark,
>
>I'm not sure if you're the right person to inform about this, but we believe
>there is an error in the results produced by the
>org.apache.commons.math.distribution.BinomialDistributionImpl.cumulativeProbability(int
>numberOfSuccesses) method.
>
>When the probability of success is zero, and numberOfSuccesses is greater than
>zero, we would expect the cumulative probability to be zero. The 
>result returned
>is, however, one.
>
>org.apache.commons.math.distribution.BinomialDistributionImpl.probability(int
>numberOfSuccesses) behaves as expected.
>
>Obviously this is very easy to workaround, but I thought the development team
>should know.
>
>After significant testing on these two functions we are preparing to use the
>commons math package in a production application, and would like to thank you
>and the other members of the team for starting work on this project. We
>understand that the library is in development, and despite the extra 
>integration
>work that will be required by us as the library develops, the 
>software you have
>developed is already of great use.
>
>Best regards,
>
>David Morgan-Brown
>Deutsche Bank
>
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>
>--
>Mark Diggory
>Software Developer
>Harvard MIT Data Center
>http://www.hmdc.harvard.edu

-- 
Albert Davidson Chou

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