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https://issues.apache.org/jira/browse/LUCENE-4927?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tommaso Teofili resolved LUCENE-4927.
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Resolution: Fixed
> Prevent underflow in NB classifier likelihood calculation
> ---------------------------------------------------------
>
> Key: LUCENE-4927
> URL: https://issues.apache.org/jira/browse/LUCENE-4927
> Project: Lucene - Core
> Issue Type: Bug
> Components: modules/classification
> Affects Versions: 4.2
> Reporter: Tommaso Teofili
> Assignee: Tommaso Teofili
> Fix For: 5.0, 4.7
>
>
> Current likelihood calculation multiplies probabilities (whose values are
> between 0 and 1) thus having longish docs with unfrequent words for some
> class/category may lead to multiple _double_ multiplications to return 0 even
> if that's not the correct value (thus assigning such a class 0 probability
> too).
> Probably using loglikelihood and/or _BigDecimals_ may help.
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