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[help-GIFT] Pruning continued
From: |
Wolfgang Mueller |
Subject: |
[help-GIFT] Pruning continued |
Date: |
Mon, 3 Sep 2001 23:17:20 +0200 |
I wrote some while ago:
> It means
> the program will read the feature list for the 70% query features with the
> highest term frequency.
Oops, this is wrong. Thanks, Henning, for pointing out there was a bug in my
message. Here's the fix: the truth can be found in this line, taken from
CQInvertedFile.cc, line 650, to be precise:
//[ QFW stands for QueryFeatureWeighters ]
outQFW.sort(CSortPointers_WF <CSortByAbsQueryFactor_WF>());
In fact, we sort things by the absolute value of the "query factor" before
pruning. The query factor contains all the knowledge about the weight that
depends only on the query (and not on the retrieved document, e.g. the term
frequency of the feature in the retrieved document). In the case of a tf.idf
weight this will be tf(query).idf with tf(query) the effective term
frequency. I hope this time I got it right, please don't hesitate to correct
me.
BTW: See CWeightingFunction.h for more descriptions about the query factor.
Cheers,
Wolfgang
--
Wolfgang Müller,
assistant-doctorant == PhD student (2001), teaching assistant
Personal page: http://cui.unige.ch/~vision/members/WolfgangMueller.html
Maintainer, GNU Image Finding Tool (http://www.gnu.org/software/gift)
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