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https://issues.apache.org/jira/browse/MAHOUT-678?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sean Owen reassigned MAHOUT-678:
--------------------------------
Assignee: Ted Dunning
> 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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