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From "Martin Illecker (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAHOUT-1266) Two minor problems in DistributedRowMatrix using MatrixMultiplication
Date Wed, 19 Jun 2013 10:35:22 GMT

    [ https://issues.apache.org/jira/browse/MAHOUT-1266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13687840#comment-13687840
] 

Martin Illecker commented on MAHOUT-1266:
-----------------------------------------

Thanks Sebastian, I got it.
You are calculating A' * B not A * B.

But then it's not a matrix multiplication defined as A * B!
Normally when executing a matrix multiplication of matrix A and matrix B, you would believe
to get A * B not A' * B? 
So, how can I do a matrix multiplication (A * B) in Mahout, because I think there is no way
to get A * B from A' * B?
                
> Two minor problems in DistributedRowMatrix using MatrixMultiplication
> ---------------------------------------------------------------------
>
>                 Key: MAHOUT-1266
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-1266
>             Project: Mahout
>          Issue Type: Bug
>          Components: Math
>    Affects Versions: 0.7
>            Reporter: Martin Illecker
>            Priority: Trivial
>              Labels: newbie
>   Original Estimate: 10m
>  Remaining Estimate: 10m
>
> Hello,
> I think I have found two minor problems in *DistributedRowMatrix*.
> In [1] the condition is wrong, because (l x m) * (m x n) = (l x n).
> The condition should be like in [2]. 
> And in *times*[3] the {{this.transpose()}} seems to be missing? (See [4])
> Do you have any benchmark results for Mahout MatrixMultiplication?
> Thanks!
> Martin
> [1] [https://github.com/apache/mahout/blob/trunk/core/src/main/java/org/apache/mahout/math/hadoop/DistributedRowMatrix.java#L191-193]
> [2] [https://github.com/millecker/applications/blob/master/hadoop/rootbeer/matrixmultiplication/src/at/illecker/hadoop/rootbeer/examples/matrixmultiplication/DistributedRowMatrix.java#L221-225]
> [3] [https://github.com/apache/mahout/blob/trunk/core/src/main/java/org/apache/mahout/math/hadoop/DistributedRowMatrix.java#L190-206]
> [4] [https://github.com/millecker/applications/blob/master/hadoop/rootbeer/matrixmultiplication/src/at/illecker/hadoop/rootbeer/examples/matrixmultiplication/DistributedRowMatrix.java#L230-231]

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