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https://issues.apache.org/jira/browse/MAHOUT-678?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13088613#comment-13088613
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Hudson commented on MAHOUT-678:
-------------------------------

Integrated in Mahout-Quality #996 (See 
[https://builds.apache.org/job/Mahout-Quality/996/])
    MAHOUT-678 commit reasonable band-aid proposed in the patch to resolve the 
proximate issue: no more NPE when not running on binomial data

srowen : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1160069
Files : 
* 
/mahout/trunk/core/src/main/java/org/apache/mahout/classifier/sgd/MixedGradient.java


> NullPointerException while using MixedGradient with SGD algorithm
> -----------------------------------------------------------------
>
>                 Key: MAHOUT-678
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-678
>             Project: Mahout
>          Issue Type: Bug
>          Components: Classification
>    Affects Versions: 0.5
>            Reporter: Stanley Xu
>            Assignee: Ted Dunning
>             Fix For: 0.6
>
>         Attachments: nullpointerexceptionbugfix.diff
>
>   Original Estimate: 2h
>  Remaining Estimate: 2h
>
> I am trying to use the MixedGradient in OnlineLogisticRegression algorithm. 
> But I will get an NullPointerException randomly if I set the alpha larger 
> than 0. 
> I checked the code and found that in the RankingGradient used by 
> MixedGradient, it assume that the target category should be only 2, rather 
> than multiple. And the rank gradient should only be used once the Gradient 
> object knew both the positive and negative targets. I created a simple patch 
> to make it workable, but I am not really understand the MixedGradient method 
> deeply, please check the patch carefully to see if it really works correctly.

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