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http://issues.apache.org/bugzilla/show_bug.cgi?id=36215 Summary: [Math] HypergeometricDistributionImpl cumulativeProbability calculation overflown Product: Commons Version: Nightly Builds Platform: PC OS/Version: Windows XP Status: NEW Severity: normal Priority: P2 Component: Math AssignedTo: [email protected] ReportedBy: [EMAIL PROTECTED] Hi, 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 code really isn't up for me......hope someone can fix it, :) BTW I'm using cygwin under WinXP pro SP2, with Java SDK 1.4.2_09 build b05, and the commons-math I used is both the 1.0 and the nightly build of 8-15-05. the code: ------------------- import org.apache.commons.math.distribution.HypergeometricDistributionImpl; class HyperGeometricProbability { public static void main(String args[]) { if(args.length != 4) { System.out.println("USAGE: java HyperGeometricProbabilityCalc [population] [numsuccess] [sample] [overlap]"); } else { String population = args[0]; String numsuccess = args[1]; String sample = args[2]; String overlap = args[3]; int populationI = Integer.parseInt(population); int numsuccessI = Integer.parseInt(numsuccess); int sampleI = Integer.parseInt(sample); int overlapI = Integer.parseInt(overlap); HypergeometricDistributionImpl hDist = new HypergeometricDistributionImpl(populationI, numsuccessI, sampleI); double raw_probability = 1.0; double cumPro = 1.0; double real_cumPro = 1.0; try { if (0 < overlapI && 0 < numsuccessI && 0 < sampleI) { raw_probability = hDist.probability(overlapI); cumPro = hDist.cumulativeProbability(overlapI - 1.0); real_cumPro = 1.0 - cumPro; System.out.println("cumulative probability=" + cumPro + "\t" + "raw probability=" + raw_probability + "\t" + "real cumulative probability=" + "\t" + real_cumPro); } } catch (Exception e) { System.err.println("BAD PROBABILITY CALCULATION"); } } } } ---------------------------------- -- Configure bugmail: http://issues.apache.org/bugzilla/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are the assignee for the bug, or are watching the assignee. --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
