[jira] Commented: (MAHOUT-208) Vector.getLengthSquared() is dangerously optimized

["Jake Mannix (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAHOUT-208?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12805408#action_12805408 ] 

Jake Mannix commented on MAHOUT-208:
------------------------------------

Hmm... I'm getting bitten by this again: setQuick() mutates, but only calls "lengthSquared = -1.0" in DenseVector.  The sparse vectors don't do this, and nasty things happen. Will check in fix.

> Vector.getLengthSquared() is dangerously optimized
> --------------------------------------------------
>
>                 Key: MAHOUT-208
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-208
>             Project: Mahout
>          Issue Type: Bug
>          Components: Math
>    Affects Versions: 0.1
>         Environment: all
>            Reporter: Jake Mannix
>            Assignee: Sean Owen
>             Fix For: 0.3
>
>
> SparseVector and DenseVector both cache the value of lengthSquared, so that subsequent calls to it get the cached value.  Great, except the cache is never cleared - calls to set/setQuick or assign or anything, all leave the cached value unchanged.  
> Mutating method calls should set lengthNorm to -1 so that the cache is cleared.
> This could be a really nasty bug if hit.

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