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https://issues.apache.org/jira/browse/MATH-1684?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ruiqi Dong updated MATH-1684:
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Priority: Minor (was: Major)
> WeightedProduct should handle all-zero weights according to mathematical
> definition
> -----------------------------------------------------------------------------------
>
> Key: MATH-1684
> URL: https://issues.apache.org/jira/browse/MATH-1684
> Project: Commons Math
> Issue Type: Improvement
> Components: legacy
> Affects Versions: 4.0-beta1
> Reporter: Ruiqi Dong
> Priority: Minor
> Original Estimate: 0.5h
> Remaining Estimate: 0.5h
>
> The {{WeightedProduct}} class currently throws a
> {{MathIllegalArgumentException}} when all weights are zero, but
> mathematically this should return 1.0 as the result. When calling
> {{WeightedProduct.evaluate()}} with a weights array containing all zeros, the
> method throws MathIllegalArgumentException. According to the mathematical
> definition of weighted product: {{∏ values[i]^weights[i]. }}When all weights
> are 0, this becomes: {{∏ values[i]^0 = ∏ 1 = 1.}}
> {{}}
> *Root Cause:* The issue occurs because {{WeightedProduct.evaluate()}} calls
> {{MathArrays.verifyValues(values, weights, begin, length, true)}} where the
> last parameter requires at least one non-zero weight. This validation is
> appropriate for some weighted operations (like weighted mean) but is
> unnecessarily restrictive for weighted product.{{{}{}}}
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