[jira] [Commented] (MAHOUT-796) Modified power iterations in existing SSVD code

["Dmitriy Lyubimov (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAHOUT-796?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13091436#comment-13091436 ] 

Dmitriy Lyubimov commented on MAHOUT-796:
-----------------------------------------

current code is essentially equivalent to running this mod with q=0.

> Modified power iterations in existing SSVD code
> -----------------------------------------------
>
>                 Key: MAHOUT-796
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-796
>             Project: Mahout
>          Issue Type: Improvement
>          Components: Math
>    Affects Versions: 0.5
>            Reporter: Dmitriy Lyubimov
>            Assignee: Dmitriy Lyubimov
>              Labels: SSVD
>             Fix For: 0.6
>
>
> Nathan Halko contacted me and pointed out importance of availability of power iterations and their significant effect on accuracy of smaller eigenvalues and noise attenuation. 
> Essentially, we would like to introduce yet another job parameter, q, that governs amount of optional power iterations. The suggestion how to modify the algorithm is outlined here : https://github.com/dlyubimov/ssvd-lsi/wiki/Power-iterations-scratchpad .
> Note that it is different from original power iterations formula in the paper in the sense that additional orthogonalization performed after each iteration. Nathan points out that that improves errors in smaller eigenvalues a lot (If i interpret it right). 

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