fix: Fix stddev indeterministically producing NAN #13248
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eejbyfeldt
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In the VarianceGroupAccumulator we were missing a `count == 0` check that is present in the normal Accumulator. This mostly does not matter except for the case where the first state to be merged has `count == 0` then the `merge` function will incorrectly calculate a new m2 of NAN which will propagate to the final result. This fixes the bug bu adding the missing `count == 0` check.
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findepi
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Nov 4, 2024
| @@ -316,6 +316,7 @@ fn merge( | |||
| mean2: f64, | |||
| m22: f64, | |||
| ) -> (u64, f64, f64) { | |||
| debug_assert!(count != 0 || count2 != 0, "Cannot merge two empty states"); | |||
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I don't exactly know how it works. Is supporting this not needed?
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It is a precondition of using this function. So support is not needed here, but expected to be handled by callers. When both counts are 0 then also mean and m2 is 0 and the correct result would also be all 0.
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i should have checked the callers. thanks. 👍
findepi
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Nov 4, 2024
alamb
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Nov 5, 2024
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Which issue does this PR close?
Closes #13247
Rationale for this change
In the VarianceGroupAccumulator we were missing a
count == 0checkthat is present in the normal Accumulator. This mostly does not matter
except for the case where the first state to be merged has
count == 0then the
mergefunction will calculate a new m2 of NAN which willpropagate to the final result.
What changes are included in this PR?
This fixes the bug bu adding the missing
count == 0check.Are these changes tested?
New and existing tests.
Are there any user-facing changes?
Correctness issue is fixed.