ROOT  6.06/09
Reference Guide
CrossEntropy.cxx
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1 // @(#)root/tmva $Id$
2 // Author: Andreas Hoecker, Joerg Stelzer, Helge Voss, Kai Voss
3 
4 /**********************************************************************************
5  * Project: TMVA - a Root-integrated toolkit for multivariate data analysis *
6  * Package: TMVA *
7  * Class : TMVA::CrossEntropy *
8  * Web : http://tmva.sourceforge.net *
9  * *
10  * Description: Implementation of the CrossEntropy as separation criterion *
11  * -p log (p) - (1-p)log(1-p); p=purity *
12  * *
13  * *
14  * Authors (alphabetical): *
15  * Andreas Hoecker <Andreas.Hocker@cern.ch> - CERN, Switzerland *
16  * Helge Voss <Helge.Voss@cern.ch> - MPI-K Heidelberg, Germany *
17  * Kai Voss <Kai.Voss@cern.ch> - U. of Victoria, Canada *
18  * *
19  * Copyright (c) 2005: *
20  * CERN, Switzerland *
21  * U. of Victoria, Canada *
22  * Heidelberg U., Germany *
23  * *
24  * Redistribution and use in source and binary forms, with or without *
25  * modification, are permitted according to the terms listed in LICENSE *
26  * (http://tmva.sourceforge.net/LICENSE) *
27  **********************************************************************************/
28 
29 //_______________________________________________________________________
30 //
31 // Implementation of the CrossEntropy as separation criterion
32 // -p log (p) - (1-p)log(1-p); p=purity
33 //_______________________________________________________________________
34 
35 #include "TMath.h"
36 #include "TMVA/CrossEntropy.h"
37 
39 
40 ////////////////////////////////////////////////////////////////////////////////
41 /// Cross Entropy defined as
42 /// -p log (p) - (1-p)log(1-p); p=purity = s/(s+b)
43 
44 Double_t TMVA::CrossEntropy::GetSeparationIndex( const Double_t &s, const Double_t &b )
45 {
46  if (s+b <= 0) return 0;
47  Double_t p = s/(s+b);
48  if (p<=0 || p >=1) return 0;
49  // return - ( p * log (p) + (1-p)*log(1-p) );
50  return - ( p * TMath::Log2(p) + (1-p)*TMath::Log2(1-p) );
51 }
Double_t Log2(Double_t x)
Definition: TMath.cxx:104
ClassImp(TMVA::CrossEntropy) Double_t TMVA
Cross Entropy defined as -p log (p) - (1-p)log(1-p); p=purity = s/(s+b)
double Double_t
Definition: RtypesCore.h:55
Abstract ClassifierFactory template that handles arbitrary types.