TwoOffShellCalculator.cc
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TwoOffShellCalculator.cc
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	// -- C++ --
	//
	// TwoOffShellCalculator.cc is a part of Herwig++ - A multi-purpose Monte Carlo event generator
	// Copyright (C) 2002-2007 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.
	//
	//
	// This is the implementation of the non-inlined, non-templated member
	// functions of the TwoOffShellCalculator class.
	//

	#include "TwoOffShellCalculator.h"
	#include "ThePEG/Interface/ClassDocumentation.h"

	using namespace Herwig;

	// calculate the width for a given mass
	Energy TwoOffShellCalculator::partialWidth(Energy2 q2) const {
	TwoOffShellIntegrand integrand(this,sqr(_massptr->nominalMass()),
	_massptr->nominalWidth()*_massptr->nominalMass());
	_scale=q2;
	// the limits
	Energy upp=min(sqrt(q2)-_mother,_massptr->upperLimit());
	Energy low=max(_minmass,_massptr->lowerLimit());
	if(low>upp) return ZERO;
	// transform the limits of BW smoothing
	Energy2 mass2 =_massptr->nominalMass()*_massptr->nominalMass();
	Energy2 mwidth =_massptr->nominalMass()*_massptr->nominalWidth();
	double rhomin=atan((low*low-mass2)/mwidth);
	double rhomax=atan((upp*upp-mass2)/mwidth);
	return _integrator.value(integrand,rhomin,rhomax);
	}