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From Sean Owen <sro...@gmail.com>
Subject Re: Recommender's formula
Date Mon, 26 Nov 2012 20:45:56 GMT
Both are implemented in the project, and both are mentioned in a lot
of papers. Pearson correlation and cosine similarity aren't specific
to recommenders. Mean centering is generally a good idea and is what I
would recommend, but it's your choice. Both are options so there is
not somehow one version that is implemented in the project. You could
use either.

On Mon, Nov 26, 2012 at 7:10 PM, Evgeny Karataev
<karataev.evgeny@gmail.com> wrote:
> Hello,
>
> I've read Mahout in Action book; then  this paper - "Case Study Evaluation
> of Mahout as a Recommender Platform" (
> http://ir.ii.uam.es/rue2012/papers/rue2012-seminario.pdf);  and then this
> Sean Owen's comment (
> http://mail-archives.apache.org/mod_mbox/mahout-user/201210.mbox/%3CCAEccTyzRzhRzUi9FGCPhPqa01bei=wYCtX2kewOcpfvU37PPGw@mail.gmail.com%3E)
> and now I am confused what formula is used for user-based (and
> item-based) recommendations. What paper is it based on?
>
> Does it use mean centering as in the formula in Resnick's paper (
> http://dl.acm.org/citation.cfm?id=192905) or formula 4.15 in "A
> Comprehensive Survey of Neighborhood-based Recommendation Methods" (
> http://www.springerlink.com/content/n3jq77686228781n/)? Or authors of "Case
> Study Evaluation of Mahout as a Recommender Platform" are right and it
> computed recommendation somehow similar to formula 4.12 in "A Comprehensive
> Survey of Neighborhood-based Recommendation Methods"?
>
>
> Following the algorithm in the Mahout in Action book, does not seem like i
> uses mean centering. However, in the section about Cosine similarity,
> authors states that the input it mean centered.
>
>
> Thank you.
>
> --
> Best Regards,
> Evgeny Karataev

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