[jira] [Commented] (MAHOUT-638) Stochastic svd's is not handling well all cases of sparse vectors

["Dmitriy Lyubimov (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAHOUT-638?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13092649#comment-13092649 ] 

Dmitriy Lyubimov commented on MAHOUT-638:
-----------------------------------------

This  of course is still wrong. I looked at the implementAtion of the full iterator in sparse vectors and it does sequential iteration, whereas I assumed it is equivAlent to iteratenonzero. So this fix is not the right one and sparse inputs are still handled deficiently. 

I cannot reopen this one, so I will commit the quick fix for that in one of the other re lated issues.


> Stochastic svd's is not handling well all cases of sparse vectors 
> ------------------------------------------------------------------
>
>                 Key: MAHOUT-638
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-638
>             Project: Mahout
>          Issue Type: Bug
>          Components: Math
>    Affects Versions: 0.5
>            Reporter: Dmitriy Lyubimov
>            Assignee: Dmitriy Lyubimov
>             Fix For: 0.5
>
>         Attachments: MAHOUT-622-2.patch, MAHOUT-638-2.patch, MAHOUT-638-2.patch, MAHOUT-638.patch
>
>
> The Mahout patch of the algorithm is not handling all types of sparse input efficiently. BtJob doesn't handle SequentialSparseVector in a way to pick only non-zero elements from initial input and QJob doesn't iterate over RandomAccessSparseVector correctly. With extremely sparse inputs (0.05% non-zero elements) that leads to a terrible inefficiency in the aforementioned jobs (QJob, BtJob).

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