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https://issues.apache.org/jira/browse/MAHOUT-1266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13687841#comment-13687841
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Sebastian Schelter commented on MAHOUT-1266:
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Yes, the name of the job is misleading, but the javadoc says it computes A'*B.
You can do A*B either by first transposing A via
org.apache.mahout.math.hadoop.TransposeJob or by simply storing A' when you
create your sequence files.
> 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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