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GaussianIntegrator.h
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// -*- C++ -*-
//
// GaussianIntegrator.h is a part of Herwig - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2019 The Herwig Collaboration
//
// Herwig is licenced under version 3 of the GPL, see COPYING for details.
// Please respect the MCnet academic guidelines, see GUIDELINES for details.
//
#ifndef HERWIG_GaussianIntegrator_H
#define HERWIG_GaussianIntegrator_H
//
// This is the declaration of the GaussianIntegrator class.
//
#include "ThePEG/Pointer/ReferenceCounted.h"
#include "ThePEG/Repository/CurrentGenerator.h"
#include <vector>
namespace Herwig {
using namespace ThePEG;
/** \ingroup Utilities
* \author Peter Richardson
* This class is designed to perform the integral of a function
* using Gaussian quadrature.The method is adaptive based on using 6th,12th,
* 24th,48th, or 96th order Gaussian quadrature combined with
* subdivision of the integral if this is insufficient.
*
* The class is templated on a simple class which should provide a
* T::operator () (double) const which provides the integrand for the function.
*/
class GaussianIntegrator : public Pointer::ReferenceCounted {
public:
/** @name Standard constructors and destructors. */
//@{
/**
* Default Constructor
*/
GaussianIntegrator()
: _abserr(1.E-35), _relerr(5.E-5), _binwidth(1.E-5), _maxeval(100000) {
// setup the weights and abscissae
Init();
}
/**
* Specify all the parameters.
* @param abserr Absolute error.
* @param relerr Relative error.
* @param binwidth Width of the bin as a fraction of the integration region.
* @param maxeval Maximum number of function evaluations
*/
GaussianIntegrator(double abserr, double relerr, double binwidth,
int maxeval)
: _abserr(abserr), _relerr(relerr),
_binwidth(binwidth),
_maxeval(maxeval) {
// setup the weights and abscissae
Init();
}
/// helper type for the integration result
template <class T>
using ValT = decltype(std::declval<typename T::ValType>()
* std::declval<typename T::ArgType>());
/**
* The value of the integral
* @param lower The lower limit of integration.
* @param upper The upper limit of integration.
*/
template <class T>
inline ValT<T> value(const T &,
const typename T::ArgType lower,
const typename T::ArgType upper) const;
private:
/**
* The assignment operator is private and must never be called.
* In fact, it should not even be implemented.
*/
GaussianIntegrator & operator=(const GaussianIntegrator &) = delete;
/**
* Initialise the weights and abscissae.
*/
void Init();
private:
/**
* The weights for the gaussian quadrature.
*/
std::vector< std::vector<double> > _weights;
/**
* The abscissae.
*/
std::vector< std::vector <double> > _abscissae;
/**
* The parameters controlling the error.
*/
double _abserr,_relerr;
/**
* The minimum width of a bin as a fraction of the integration region.
*/
double _binwidth;
/**
* Maximum number of function evaluations.
*/
int _maxeval;
};
}
#include "GaussianIntegrator.tcc"
#endif /* HERWIG_GaussianIntegrator_H */

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