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RhoDMatrix.h
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// -*- C++ -*-
//
// RhoDMatrix.h is a part of ThePEG - Toolkit for HEP Event Generation
// Copyright (C) 2003-2011 Peter Richardson, Leif Lonnblad
//
// ThePEG is licenced under version 2 of the GPL, see COPYING for details.
// Please respect the MCnet academic guidelines, see GUIDELINES for details.
//
#ifndef ThePEG_RhoDMatrix_H
#define ThePEG_RhoDMatrix_H
// This is the declaration of the RhoDMatrix class.
#include "ThePEG/PDT/PDT.h"
#include "ThePEG/Helicity/HelicityDefinitions.h"
#include <cassert>
namespace ThePEG {
/**
* The RhoDMatrix class is designed to implement the storage of the
* rho and D matrices which are required for the spin correlation
* algorithm. The matrix stores the spin as 2s+1.
*
* @author Peter Richardson
*
*/
class RhoDMatrix {
public:
/** @name Standard constructors and destructors. */
//@{
/**
* Default constructor with undefined spin.
*/
RhoDMatrix() : _spin(), _ispin() {}
/**
* Standard constructor giving the spin as 2s+1. The matrix starts out averaged,
* unless the second argument is false, when it is zeroed.
*/
RhoDMatrix(PDT::Spin inspin, bool average = true)
: _spin(inspin), _ispin(abs(int(inspin))) {
assert(_ispin <= MAXSPIN);
// initialize to average
for(size_t ix=0; ix<_ispin; ++ix)
for(size_t iy=0; iy<_ispin; ++iy)
_matrix[ix][iy] = (average && ix==iy) ? 1./_ispin : 0.;
}
//@}
public:
/** @name Access matrix elements. */
//@{
/**
* Return an element of the matrix.
*/
Complex operator() (size_t ix, size_t iy) const {
assert(ix < _ispin);
assert(iy < _ispin);
return _matrix[ix][iy];
}
/**
* Set an element of the matrix.
*/
Complex & operator() (size_t ix, size_t iy) {
assert(ix < _ispin);
assert(iy < _ispin);
return _matrix[ix][iy];
}
/**
* renormalise the matrix so it has unit trace
*/
void normalize() {
#ifndef NDEBUG
static const double epsa=1e-30, epsb=1e-10;
#endif
Complex norm = 0.;
for(size_t ix=0; ix<_ispin; ++ix)
norm += _matrix[ix][ix];
assert(norm.real() > epsa);
assert(norm.imag()/norm.real() < epsb);
double invnorm = 1./norm.real();
for(size_t ix=0; ix<_ispin; ++ix)
for(size_t iy=0; iy<_ispin; ++iy)
_matrix[ix][iy]*=invnorm;
}
//@}
/** @name Access the spin. */
//@{
/**
* Get the spin. The spin is returned as 2J+1 in units of hbar/2.
*/
PDT::Spin iSpin() const { return _spin; }
//@}
/**
* Output the spin density matrix for debugging purposes.
*/
friend ostream & operator<<(ostream & os, const RhoDMatrix & rd);
private:
/**
* 2s+1 for the particle.
*/
PDT::Spin _spin;
/**
* Storage of 2s+1 for speed.
*/
size_t _ispin;
/**
* Spin matrix size
*/
enum { MAXSPIN = 5 };
/**
* Storage for the matrix allowing up to spin 2 particles.
*/
// Deliberately not using vector<> to avoid calls to 'new'
// from this commonly used class.
Complex _matrix[MAXSPIN][MAXSPIN];
};
/** Output operator */
inline ostream & operator<<(ostream & os, const RhoDMatrix & rd) {
for (size_t ix = 0; ix < rd._ispin; ++ix) {
for (size_t iy = 0; iy < rd._ispin; ++iy)
os << rd._matrix[ix][iy] << " ";
os << '\n';
}
return os;
}
}
#endif /* ThePEG_RhoDMatrix_H */

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