[jira] [Commented] (LUCENE-4927) Prevent underflow in NB classifier likelihood calculation

["ASF subversion and git services (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-4927?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13829794#comment-13829794 ] 

ASF subversion and git services commented on LUCENE-4927:
---------------------------------------------------------

Commit 1544433 from [~teofili] in branch 'dev/trunk'
[ https://svn.apache.org/r1544433 ]

LUCENE-4927 - switched to log prior/likelihood to avoid possible underflows

> 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
>
>
> 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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