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Entropy.h

Go to the documentation of this file.

#ifndef Impala_Core_Histogram_Entropy_h
#define Impala_Core_Histogram_Entropy_h

#include "Core/Histogram/Histogram1dTem.h"
#include <math.h>

namespace Impala
{
namespace Core
{
namespace Histogram
{

// this code is a translation of Jaspers implementation.
// for now only with integer histograms, is the same thing possible with
// contiuous values?
double
Entropy(const Histogram::Histogram1dTem<int>* hist)
{
    const double cLog2 = log(2.); // used for log with base 2
    double sum = hist->TotalWeight();
    if(sum == 0)
        return 0.;
    double e=0;
    for(int i=0 ; i<hist->Size() ; ++i)
    {
        double d = hist->Elem(i);
        if(d>0)
        {
            d /= sum;
            e -= d * (log(d)/cLog2);
        }
    }
    return e;
}    

} // namespace Histogram
} // namespace Core
} // namespace Impala

#endif

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