[Math] HypergeometricDistributionImpl cumulativeProbability calculation overflown

[zhanzhi hu <mi...@gmail.com>]

Hi all, for all that might use this class:

several things I found when using this class to calculate the
cumulative probability. I attached my code FYI. three things:

1. when I used my code to calculate the cumulativeProbability(50) of
5000 200 100 (Population size, number of successes, sample size),
result was greater than 1 (1.0000000000134985);
2. when I calculated cumulativeProbability(50) and
cumulativeProbability(51) for the distribution 5000 200 100, I got the
same results, but it should have been different;
2. the cumulativeProbability(x) returns "for this distribution, X,
P(X<=x)", but most of the time (at least in my case) what I care about
is the upper tail (X>=x). based on the above findings, I can't simply
use 1-cumulativeProbability(x-1) to get what I want.

here's what I think might be related to the problem: since the
cumulativeProbability is calculating the lower tail (X<=x), a
distribution like above often has this probability very close to 1;
thus it's difficult to record a number that = 1-1E-50 'cause all you
can do is record sth like 0.9999..... and further digits will be
rounded. to avoid this, I suggest adding a new function to calculate
upper tail or change this to calculate x in a range like (n<=x<=m), in
addition to fix the overflow of the current function.

thank you for your patience to get here. I'm a newbie but I've asked
Java experts in our lab about this. looking into the source really
isn't up for me......hope someone can fix it, :)

Re: [Math] HypergeometricDistributionImpl cumulativeProbability calculation overflown

[zhanzhi hu <mi...@gmail.com>]

thanks for the tip. for all that might be interested in this bug, I've
reported to bugzilla as Bug 36215.

On 8/16/05, sebb <se...@gmail.com> wrote:
> On 16/08/05, zhanzhi hu <mi...@gmail.com> wrote:
> > Hi all, for all that might use this class:
> >
> > several things I found when using this class to calculate the
> > cumulative probability. I attached my code FYI. three things:
> 
> The code did not reach the list.
> 
> May I suggest you create a Bugzilla issue, and attach the code there?
> 
> http://issues.apache.org/bugzilla/enter_bug.cgi?product=Commons
> 
> It's a lot easier to keep track of bugs there than in mailing lists.
> 
> [snip]
>

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Re: [Math] HypergeometricDistributionImpl cumulativeProbability calculation overflown

[sebb <se...@gmail.com>]

On 16/08/05, zhanzhi hu <mi...@gmail.com> wrote:
> Hi all, for all that might use this class:
> 
> several things I found when using this class to calculate the
> cumulative probability. I attached my code FYI. three things:

The code did not reach the list.

May I suggest you create a Bugzilla issue, and attach the code there?

http://issues.apache.org/bugzilla/enter_bug.cgi?product=Commons

It's a lot easier to keep track of bugs there than in mailing lists.

[snip]

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