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From: Robert Muir <rcmuir@gmail.com>
Date: Sat, 3 Nov 2012 20:53:22 -0400
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Subject: Re: Using new similarities in Lucene 4.0
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On Tue, Oct 30, 2012 at 10:20 AM, parnab kumar <parnab.2007@gmail.com> wrote:
> Hi all,
>
>       Lucene 4 has introduced several state of the art ranking functions. I
> was wondering how could i make use of those similarities .

IndexSearcher.setSimilarity(new XYZSimilarity());

> These models
> obviously uses some more term and collection statistics as opposed to
> the traditional Vector Space Model . I guess these statistics
> are  precomputed during indexing .Should there be any changes to the
> indexing mechanism ,like specifying the indexing options to make use of
> these models .

>From the CHANGES.txt:

"All models default to the same index-time norm encoding as
DefaultSimilarity, so you can easily try these out/switch back and
forth/run experiments and comparisons without reindexing. Note: most
of the models do rely upon index statistics that are new in Lucene
4.0, so for existing 3.x indexes its a good idea to upgrade your index
to the new format with IndexUpgrader first. "

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