kalpa rajadurai wrote:
> Hi Team,
>
> We are working on a small project in designing a web based statistical
> calculator, supporting certain distribution functions.
>
> we used method *cummulativeProbability(double x)* of *class
> NormalDistributionImpl* for implementing Normal distribution function.
>
> We tried to cross check Apache API's result with that of OpenOffice Calc and
> Excel's result. In most of the cases, the results matched with each other.
> But in certain rare cases, the cumulativeProbability() method returned by
> slightly different result when compared to the result returned by NORMDIST()
> function of openoffice calc and Excel.
>
> Here goes the illustration of the case where we found the mismatch in
> results:
>
> *Using Apache's API:*
> NormalDistribution normDist = new NormalDistributionImpl(40,1.5)
> ;
> try{
> System.out.println("cummulative probability::
> "+normDist.cumulativeProbability(0.908789));
> }
> catch(MathException e){
> e.printStackTrace();
> }
>
> *Result:*
> cummulative probability:: *8.104628079763643E15*
>
> *Using openoffice calc:*
> Same input values given in openoffice calc using the formula:
> *=NORMDIST(0.908789;40;1.5;1)*
>
> *Result:*
> *0.0*
>
> *Using Microsoft Excel:*
> Same input values given in excel using the formula:
> *=NORMDIST(0.908789;40;1.5;1)*
>
> *Result:*
> *5.0738E150*
>
> *Different results:*
> Apache 8.104628079763643E15
> Openoffice 0.0
> Excel 5.0738E150
>
> We wish to know the following things,
> 1.) What is the reason for this variation in results?
The difference is due to different numeric algorithms used to
approximate the cumulative probabilities  in particular how extreme
values are handled. The probability in the example is very close to
zero  all three agree on that.
> 2.) Which result is more accurate?
Excel is likely the best answer; though the only confirmation that I
can give of that is that R gives the same answer and the correct
answer is certainly positive. The worst answer is the one reported
by commonsmath. The value should not be negative. This is likely
related to an open bug (MATH301). Thank you for reporting this.
> 3.) Is there any possibility to get the same results as Open Office or Excel
> for this case, using Apache's API?
Commons Math 2.1 will correct the bug mentioned above, so we will
return either 0 or a positive value for this and other extreme tail
probabilities.
Thanks again for pointing out the discrepancy.
Phil
>
> Hope to receive reply from your team at the earliest as possible.
> Thanks in Advance
>

To unsubscribe, email: userunsubscribe@commons.apache.org
For additional commands, email: userhelp@commons.apache.org
