Fixing KDE evaluate() to return correct ValueAndMagnitude object #128602
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…ct for bandwidth = 0 Prior to this change, the evaluate method would return a dummy object for an input with bandwidth = 0. This would occur if the dataset had zero variance (see KDE constructor). This would then cause ChangePointDetector to fail to detect a spike on a dataset containing all equal numbers except for one spike. This change removes the bandwidth = 0 condition for returning a dummy ValueAndMagnitude object. Statistical testing in ChangePointDetector now properly detects the spike in the example mentioned above. Unit tests are added to confirm the bug is fixed.
elasticsearchmachine
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nielsbauman
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Pinging @elastic/ml-core (Team:ML) |
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@elasticmachine test this please |
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Thanks for your contribution @Jason-Whitmore and thanks for adding the tests, we will try to review this as soon as possible |
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@elasticmachine test this please |
tveasey
reviewed
Oct 9, 2025
x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/aggs/changepoint/KDE.java
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This change enables an early return and avoids numerical issues.
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Issue #127517 describes
ChangePointDetector.getChangeType()failing to detect a spike when all non spike values are constant (for example, the input [51,51,...,51,50001,51...,51]).Prior to this change, the
KDE.evaluate()method would return a special object for an input withbandwidth == 0. This would occur if the values excluding the spike had zero variance (seeKDEconstructor). This would then causeChangePointDetector.getChangeType()andSpikeAndDipDetector.detect()to use the wrong p-value and fail to detect the spike.This change removes the
bandwidth == 0condition for returning a specialValueAndMagnitudeobject. Statistical testing inChangePointDetector.getChangeType()andSpikeAndDipDetector.detect()now properly detect the spike in the example mentioned above.Unit tests are added to confirm the bug is fixed.
Closes #127517