[jira] Updated: (MAHOUT-421) Item similarity in AbstractSimilarity always centers data

["Sean Owen (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MAHOUT-421?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sean Owen updated MAHOUT-421:
-----------------------------

             Assignee: Sean Owen
    Affects Version/s: 0.4
             Priority: Minor  (was: Major)

Sounds good, I think it's largely because un-centering is the exception and isn't used for user-user similarity as it happens, yet. Easy enough to change this however.

> Item similarity in AbstractSimilarity always centers data
> ---------------------------------------------------------
>
>                 Key: MAHOUT-421
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-421
>             Project: Mahout
>          Issue Type: Bug
>          Components: Collaborative Filtering
>    Affects Versions: 0.4
>            Reporter: Emerson Murphy-HIll
>            Assignee: Sean Owen
>            Priority: Minor
>
> I'm trying to use UncenteredCosineSimilarity. When calculating similarity between users in AbstractSimilarity>>itemSimilarity, there's a condition to determine whether to center the data:
> double result;
> if (centerData) {
>   ... get result with centering
> } else {
>    ... get result without
> }
>    
> In AbstractSimilarity>>itemSimilarity, there's no conditional. It *always* centers the data. Shouldn't it only center the data when centerData is true?

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