(I can easily make the fix and add a test, but is the right thing to
return 0, or instead proceed in the method with the value -sqrt(-llr)
when llr is negative?)
On Thu, Apr 29, 2010 at 12:44 PM, Shashikant Kore <shashik...@gmail.com> wrote:
> Root LLR calculation has a minor bug. When LLR score is negative,
> square root is undefined. You can see the result for the following to
> be NaN.
>
> org.apache.mahout.math.stats.LogLikelihood.rootLogLikelihoodRatio(6,
> 7567, 1924, 2426487)
>
> A minor fix would be to return zero if LLR is less than zero as follows.
>
> public static double rootLogLikelihoodRatio(int k11, int k12, int k21,
> int k22) {
> double llr = logLikelihoodRatio(k11, k12, k21, k22);
> if (llr < 0)
> return 0;
> return Math.signum(((double) k11 / (k11+k12)) - ((double) k21 /
> (k21+k22))) * Math.sqrt(llr);
> }
>
> --shashi
>
