[GitHub] [commons-statistics] aherbert commented on pull request #26: Add truncated normal distribution.

[GitBox <gi...@apache.org>]

aherbert commented on pull request #26:
URL: https://github.com/apache/commons-statistics/pull/26#issuecomment-782051472


   Thanks for the contribution. The implementation and tests look good (all edge cases are covered).
   
   The code is currently failing PMD checks. Most of these are for missing the `final` keyword on local variables. You can see the PMD errors by running:
   ```
   mvn pmd:pmd
   ```
   Then open the file in `target/site/pmd.html`
   
   There is also an error for a confusing ternary. I think it is OK in this context but to avoid the issue what do you think to rewriting the constructor as:
   ```java
           if (lower == Double.NEGATIVE_INFINITY) {
               if (upper == Double.POSITIVE_INFINITY) {
                   // No truncation
                   this.mean = mean;
                   variance = sd * sd;
               } else {
                   // One-sided lower tail truncation
                   double betaRatio = pdfBeta / cdfBeta;
                   this.mean = mean - sd * betaRatio;
                   variance = sd * sd * (1 - beta * betaRatio - betaRatio * betaRatio);
               }
           } else {
               if (upper == Double.POSITIVE_INFINITY) {
                   // One-sided upper tail truncation
                   double alphaRatio =  pdfAlpha / cdfDelta;
                   this.mean = mean + sd * alphaRatio;
                   variance = sd * sd * (1 + alpha * alphaRatio - alphaRatio * alphaRatio);
               } else {
                   // Two-sided truncation
                   this.mean = mean + pdfCdfDelta * parentSd;
                   variance = sd * sd * (1 + alphaBetaDelta - pdfCdfDelta * pdfCdfDelta);
               }
           }
   ```


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