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