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Posted to dev@mahout.apache.org by "Dmitriy Lyubimov (JIRA)" <ji...@apache.org> on 2013/07/30 01:05:49 UTC
[jira] [Commented] (MAHOUT-1298) SparseRowMatrix,SparseColMatrix:
optimize transpose()
[ https://issues.apache.org/jira/browse/MAHOUT-1298?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13723104#comment-13723104 ]
Dmitriy Lyubimov commented on MAHOUT-1298:
------------------------------------------
actually these matrices do not seem to have an optimized times() either.
> SparseRowMatrix,SparseColMatrix: optimize transpose()
> -----------------------------------------------------
>
> Key: MAHOUT-1298
> URL: https://issues.apache.org/jira/browse/MAHOUT-1298
> Project: Mahout
> Issue Type: New Feature
> Components: Math
> Affects Versions: 0.8
> Reporter: Dmitriy Lyubimov
> Assignee: Dmitriy Lyubimov
> Fix For: 0.9
>
>
> these matrices lack optimized transpose and rely onto AbstractMatrix's O(mn) implementation which is not cool for very sparse subblocks.
> proposal is to implement a custom transpose with two things in mind:
> 1) transpose result to row sparse matrix should be col sparse matrix, and vice versa (and not from default like() as default implementation would take);
> 2) obviously, iterate only thru non-zero elements only of all rows(columns).
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