Github user WeichenXu123 commented on a diff in the pull request: https://github.com/apache/spark/pull/19029#discussion_r135186430 --- Diff: mllib/src/main/scala/org/apache/spark/ml/stat/Summarizer.scala --- @@ -438,6 +438,10 @@ private[ml] object SummaryBuilderImpl extends Logging { while (i < len) { realVariance(i) = (currM2n(i) + deltaMean(i) * deltaMean(i) * weightSum(i) * (totalWeightSum - weightSum(i)) / totalWeightSum) / denominator + // Because of numerical error, it is possible to get negative real variance + if (realVariance(i) < 0.0) { --- End diff -- Hmm.. `WeightedLeastSquares` use another way to compute variance `Var(X) = E(X^2) - E(X)^2`. But it seems also possible to have this problem.
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