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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAHOUT-1837) Sparse/Dense Matrix analysis for Matrix Multiplication
Date Fri, 26 Aug 2016 01:06:21 GMT

    [ https://issues.apache.org/jira/browse/MAHOUT-1837?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15438237#comment-15438237
] 

ASF GitHub Bot commented on MAHOUT-1837:
----------------------------------------

GitHub user andrewpalumbo opened a pull request:

    https://github.com/apache/mahout/pull/252

    MAHOUT-1837: Fixed dense bug in drm/package.blockify()

    Create a `SparseRowMatrix` by default in order to keep `OOM` errors from occurring in
`blockify()` per conversation  in: https://github.com/apache/mahout/commit/727e5be85c0326d9c009d9cdc361fe47ffa201ad#commitcomment-18771603.
 run `densityAnalysis()` on that and convert to dense if requirements are met.

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/andrewpalumbo/mahout MAHOUT-1837-dense-bug

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/mahout/pull/252.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #252
    
----
commit 5d2f5cc9746f968d0c776f869070dd9a439de9f1
Author: Andrew Palumbo <apalumbo@apache.org>
Date:   2016-08-26T00:58:57Z

    fixed dense bug in drm/package.blockify()

----


> Sparse/Dense Matrix analysis for Matrix Multiplication
> ------------------------------------------------------
>
>                 Key: MAHOUT-1837
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-1837
>             Project: Mahout
>          Issue Type: Improvement
>          Components: Math
>    Affects Versions: 0.12.0
>            Reporter: Andrew Palumbo
>            Assignee: Andrew Palumbo
>             Fix For: 0.13.0
>
>         Attachments: compareDensityTest.ods
>
>
> In matrix multiplication, Sparse Matrices can easily turn dense and bloat memory,  one
fully dense column and one fully dense row can cause a sparse %*% sparse operation have a
dense result.  
> There are two issues here one with a quick Fix and one a bit more involved:
>    #  in {{ABt.Scala}} use check the `MatrixFlavor` of the combiner and use the flavor
of the Block as the resulting Sparse or Dense matrix type:
> {code}
> val comb = if (block.getFlavor == MatrixFlavor.SPARSELIKE) {
>               new SparseMatrix(prodNCol, block.nrow).t
>             } else {
>               new DenseMatrix(prodNCol, block.nrow).t
>             }
> {code}
>  a simlar check needs to be made in the {{blockify}} transformation.
>  
>    #  More importantly, and more involved is to do an actual analysis of the resulting
matrix data in the in-core {{mmul}} class and use a matrix of the appropriate Structure as
a result. 



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