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https://issues.apache.org/jira/browse/MAHOUT-1266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13687820#comment-13687820
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Sebastian Schelter commented on MAHOUT-1266:
--------------------------------------------
Matlab says, Mahout's result is correct:
{noformat}
>> A = [9 4 1 9;
1 8 6 3;
8 3 3 9;
7 1 9 6]
A =
9 4 1 9
1 8 6 3
8 3 3 9
7 1 9 6
>> B = [2 1 6 5;
7 8 9 5;
2 1 5 8;
7 4 4 9]
B =
2 1 6 5
7 8 9 5
2 1 5 8
7 4 4 9
>> A'*B
ans =
90 53 131 177
77 75 115 93
113 88 111 140
99 66 150 186
{noformat}
> 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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