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From Richard Simon Just <i...@richardsimonjust.co.uk>
Subject Re: Understanding the SVD recommender
Date Wed, 09 Jun 2010 18:19:05 GMT


On 04/06/10 08:53, Ted Dunning wrote:
> On Fri, Jun 4, 2010 at 12:38 AM, Sean Owen<srowen@gmail.com>  wrote:
>
>    
>> They also add on the "row" average to make a prediction, which is the
>> average rating by the user, I'm guessing -- "row" is a row of A?
>>      
>
> I would guess so, but that would only make sense if they subtracted it ahead
> of time.  In general, I don't see the point for that.  I would rather cosine
> normalize each user row.
>
>
>    

I don't know enough yet to comment on what works best, but I can give 
some evidence that they do subtract teh row average ahead of time. 
Sarwar's previous work, Application of Dimensionality Reduction piece 
(http://www.grouplens.org/papers/pdf/webKDD00.pdf) uses the same 
prediction function. In section 4.3.1 Prediction Experiment they discuss 
the removal of the row average before the SVD computation and it's later 
addition for the prediction. I'd make the assumption that the 
incremental SVD paper builds on this.

- Richard

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