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https://issues.apache.org/jira/browse/MAHOUT-165?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12781165#action_12781165
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Jake Mannix commented on MAHOUT-165:
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bq. +1 yes the order of dependency makes the most sense; also makes it easy for 
others to reuse who are interested in only the matrix library.

+1 from me as well.  This also makes it easier to keep decomposer decoupled - 
it can depend on mahout-matrix, and not need mahout-core.

But what about Vector?  Vector coming out of Core and moving into another 
module, well, everything depends on Vector, doesn't it?  In what way does this 
help?

> Using better primitives hash for sparse vector for performance gains
> --------------------------------------------------------------------
>
>                 Key: MAHOUT-165
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-165
>             Project: Mahout
>          Issue Type: Improvement
>          Components: Matrix
>    Affects Versions: 0.2
>            Reporter: Shashikant Kore
>            Assignee: Grant Ingersoll
>             Fix For: 0.3
>
>         Attachments: colt.jar, mahout-165-18nov-updated.patch, 
> mahout-165-18nov.patch, MAHOUT-165-colt.patch, mahout-165-trove.patch, 
> MAHOUT-165-updated.patch, MAHOUT-165-with-colt-module.patch, 
> MAHOUT-165-with-colt.patch, mahout-165.patch, MAHOUT-165.patch, 
> mahout-165.patch
>
>
> In SparseVector, we need primitives hash map for index and values. The 
> present implementation of this hash map is not as efficient as some of the 
> other implementations in non-Apache projects. 
> In an experiment, I found that, for get/set operations, the primitive hash of 
>  Colt performance an order of magnitude better than OrderedIntDoubleMapping. 
> For iteration it is 2x slower, though. 
> Using Colt in Sparsevector improved performance of canopy generation. For an 
> experimental dataset, the current implementation takes 50 minutes. Using 
> Colt, reduces this duration to 19-20 minutes. That's 60% reduction in the 
> delay. 

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