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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAHOUT-1960) Flipped sign in the SparseSparseDrmTimer.mscala causes Desnse Matrix multiplication
Date Mon, 27 Mar 2017 16:51:42 GMT

    [ https://issues.apache.org/jira/browse/MAHOUT-1960?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15943617#comment-15943617
] 

ASF GitHub Bot commented on MAHOUT-1960:
----------------------------------------

Github user asfgit closed the pull request at:

    https://github.com/apache/mahout/pull/298


> Flipped sign in the SparseSparseDrmTimer.mscala causes Desnse Matrix multiplication
> -----------------------------------------------------------------------------------
>
>                 Key: MAHOUT-1960
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-1960
>             Project: Mahout
>          Issue Type: Bug
>    Affects Versions: 0.13.0
>            Reporter: Andrew Palumbo
>            Assignee: Andrew Palumbo
>            Priority: Blocker
>             Fix For: 0.13.0
>
>
> In {{SparseSparseDrmTimer.mscala}} with the signature: 
>  def timeSparseDRMMMul(m: Int, n: Int, s: Int, para: Int, pctDense: Double = .20, seed:
Long = 1234L): Long = {
> the {{pctDense}} argument indicates the percent of nonZero elements in the matrix. 
> As is the code to produce a random DRM for testing is as follows:
> {code}
>   val drmA = drmParallelizeEmpty(m , s, para).mapBlock(){
>        case (keys,block:Matrix) =>
>          val R =  scala.util.Random
>          R.setSeed(seed)
>          val blockB = new SparseRowMatrix(block.nrow, block.ncol) 
>          blockB := {x => if (R.nextDouble > pctDense) R.nextDouble else x }
>        (keys -> blockB)
> }
> {code}
> The greater than sign in line:
>     blockB := {x => if (R.nextDouble > pctDense) R.nextDouble else x } 
> should be a less than sign; i.e.:
>      blockB := {x => if (R.nextDouble < pctDense) R.nextDouble else x } 
> This incorrect sign produces matrices of Incorrect density and can cause OOM errors.
>  



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