Ruiqi Dong created MATH-1684:
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Summary: 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
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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