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https://issues.apache.org/jira/browse/MAHOUT-413?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ted Dunning resolved MAHOUT-413.
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Resolution: Fixed
Sean committed a fix already.
Here is a test case to avoid regression.
> Sequential access vector has a bug in dot
> -----------------------------------------
>
> Key: MAHOUT-413
> URL: https://issues.apache.org/jira/browse/MAHOUT-413
> Project: Mahout
> Issue Type: Bug
> Reporter: Ted Dunning
>
> Zhao wrote:
> {quote}
> Hi,
> One strange thing, SequentialAccessSparseVector.dot() seems does NOT work
> correctly. When I change the Vector w = new
> RandomAccessSparseVector(Integer.MAX_VALUE, 12); Then the code works well.
> I check the source code of SequentialAccessSparseVector.dot(), it checks the
> index of two Vectors(if both of them are instance of
> SequentialAccessSparseVector), once they mis-match, it will return 0.0.
> *Why do we need such constrain?
> *
> In this case, what's the best way to get dot product between two mis-matched
> SequentialAccessSparseVector instances?
> Code:
> Vector w = new SequentialAccessSparseVector(Integer.MAX_VALUE, 12);
> w.set(1, 0.4);
> w.set(2, 0.4);
> w.set(3, -0.666666667);
> Vector v = new SequentialAccessSparseVector(Integer.MAX_VALUE, 12);
> v.set(3, 1);
> System.out.println(datastore.getFeatureRow(2).dot(w));
> The result is 0.0 (should be -0.666666667).
> {quote}
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