xapian-core  1.4.26
bo1eweight.cc
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1 
5 /* Copyright (C) 2013 Aarsh Shah
6  *
7  * This program is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU General Public License as
9  * published by the Free Software Foundation; either version 2 of the
10  * License, or (at your option) any later version.
11  *
12  * This program is distributed in the hope that it will be useful
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15  * GNU General Public License for more details.
16  *
17  * You should have received a copy of the GNU General Public License
18  * along with this program; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
22 #include <config.h>
23 
24 #include "expandweight.h"
25 #include "common/log2.h"
26 
27 using namespace std;
28 
29 namespace Xapian {
30 namespace Internal {
31 
32 double
33 Bo1EWeight::get_weight() const
34 {
35  double F = get_collection_freq();
36 
37  double N = get_dbsize();
38 
39  double mean = F / N;
40  double wt = stats.rcollection_freq * log2((1.0 + mean) / mean) + log2(1.0 + mean);
41 
42  return wt;
43 }
44 
45 }
46 }
The Xapian namespace contains public interfaces for the Xapian library.
Definition: compactor.cc:80
STL namespace.
Collate statistics and calculate the term weights for the ESet.
double log2(double x)
Definition: log2.h:31
Defines a log2() function to find the logarithm to base 2 if not already defined in the library...