[jira] [Updated] (MAHOUT-1298) SparseRowMatrix,SparseColMatrix: optimize transpose()

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

     [ https://issues.apache.org/jira/browse/MAHOUT-1298?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Dmitriy Lyubimov updated MAHOUT-1298:
-------------------------------------

    Attachment: MAHOUT-1298.path

Necessary tests seem already to be implemented.
                
> 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
>
>         Attachments: MAHOUT-1298.path
>
>
> 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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