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Statistic.h
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// -*- C++ -*-
//
// Statistic.h is a part of Herwig++ - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2011 The Herwig Collaboration
//
// Herwig++ is licenced under version 2 of the GPL, see COPYING for details.
// Please respect the MCnet academic guidelines, see GUIDELINES for details.
//
#ifndef HERWIG_Statistic_H
#define HERWIG_Statistic_H
#include <cmath>
//
// This is the declaration of the Statistic class.
//
namespace Herwig {
/**
* The Statistic class is a simple class designed to
* store a variable for statistical analysis
*/
class Statistic {
public:
/**
* The default constructor.
*/
Statistic() : _n(0), _xsum(0.), _x2sum(0.),
_min(-1e100), _max(1e100) {}
/**
* The minimum value
*/
double minimum() const { return _min; }
/**
* The maximum value
*/
double maximum() const { return _max; }
/**
* Operator to add another point
*/
void operator+=(double input)
{
++_n;
_xsum += input;
_x2sum += input * input;
if (_min > input) _min = input;
if (_max < input) _max = input;
}
/**
* Number of points
*/
unsigned int numberOfPoints() const { return _n; }
/**
* Mean
*/
double mean() const
{
return _n > 0 ? _xsum / _n : 0.;
}
/**
* Error on the mean estimate. Needed for example for Profile
* histograms, where this should be used to compute a chi2
* or significance level of deviation to data, rather than stdDeV.
* This is obvious because the error on the estimate should go to
* zero for N -> infinity.
*/
double mean_stdDev() const { return std::sqrt(mean_var()); }
/**
* Variance on the mean estimate. Needed for example for Profile
* histograms, where this should be used to compute a chi2
* or significance level of deviation to data, rather than stdDeV
* This is obvious because the error on the estimate should go to
* zero for N -> infinity.
*/
double mean_var() const
{
return _n > 1 ? var() / _n : 0.;
}
/**
* Standard Deviation
*/
double stdDev() const { return std::sqrt(var()); }
/**
* Variance
*/
double var() const
{
return _n > 1 ? ( _x2sum - _xsum*_xsum/_n ) / ( _n - 1 ) : 0.;
}
/**
* Total entry
*/
double total() const { return _xsum; }
private:
/**
* Number of entries
*/
unsigned int _n;
/**
* Sum of the values
*/
double _xsum;
/**
* Sum of the squares of the values
*/
double _x2sum;
/**
* The minimum value
*/
double _min;
/**
* The maximum value
*/
double _max;
};
}
#endif /* HERWIG_Statistic_H */

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