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https://issues.apache.org/jira/browse/SPARK-5766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14317961#comment-14317961
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Sean Owen commented on SPARK-5766:
----------------------------------

Given that RowMatrix is a row-by-row representation, it would have to be 
vector-matrix multiplication I think. In principle I think you can leverage 
native code here; the only question is whether it overcomes the overhead of the 
call for typical inputs, but it's possible.

> Slow RowMatrix multiplication
> -----------------------------
>
>                 Key: SPARK-5766
>                 URL: https://issues.apache.org/jira/browse/SPARK-5766
>             Project: Spark
>          Issue Type: Improvement
>          Components: MLlib
>            Reporter: Amaru Cuba Gyllensten
>            Priority: Minor
>              Labels: matrix
>
> Looking at the source code for RowMatrix multiplication by a local matrix, it 
> seems like it is going through all columnvectors of the matrix, doing 
> pairwise dot product on each column.  
> It seems like this could be sped up by using gemm, performing full 
> matrix-matrix multiplication on the local data, (or gemv, for vector-matrix 
> multiplication), as is done in BlockMatrix or Matrix.



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