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https://issues.apache.org/jira/browse/MAHOUT-181?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12764373#action_12764373
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Jake Mannix commented on MAHOUT-181:
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Grant, are we going to be using Ted's patch for MAHOUT-165, which he says fixes
this as well (I haven't looked in any great detail at that part to see how much
of that is covered)?
Also, is this probably going to get clobbered by any major shift toward using
commons-math linear algebra primitives?
Either way, sure, I'll bring this patch up-to-date so that we have choices.
> DistanceMeasure is broken: iteration is done over nonZeroElements of
> v1.plus(v2), not v1.minus(v2)
> --------------------------------------------------------------------------------------------------
>
> Key: MAHOUT-181
> URL: https://issues.apache.org/jira/browse/MAHOUT-181
> Project: Mahout
> Issue Type: Bug
> Components: Matrix
> Affects Versions: 0.2
> Environment: all
> Reporter: Jake Mannix
> Assignee: Grant Ingersoll
> Fix For: 0.2
>
> Attachments: MAHOUT-181.patch
>
>
> SquaredEuclideanDistanceMeasure iterates over v1.plus(v2), which has the
> right number of nonzero elements if v1.get(i) != -v2.get(i) for all i
> indexing nonzero elements, but for example, the simple case of looking at
> SquaredEuclideanDisanceMeasure.distance(v, v.assign(new NegateFunction()))
> yeilds zero on current trunk, instead of 4*v.lengthSquared().
> Attached is a patch with a unit test which checks that
> DistanceMeasure.distance always returns nonnegative results and in particular
> also does not return , as well as a fix for ManhattanDistanceMeasure,
> SquaredEuclideanDistanceMeasure, and EuclideanDistanceMeasure.
> Unfortunately, the attached unit test reveals that the
> TanimotoDistanceMeasure is more broken than I can fix at present. It doesn't
> appear to be properly using the referenced formula in wikipedia, and in fact
> sometimes returns negative results. This means that with this patch applied,
> TestTanimotoDistanceMeasure is failing (and rightfully so).
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