GhostedAreaSpec.cc

//STARTHEADER
// $Id: GhostedAreaSpec.cc 1273 2008-08-11 18:22:55Z salam $
//
// Copyright (c) 2005-2006, Matteo Cacciari and Gavin Salam
//
//----------------------------------------------------------------------
// This file is part of FastJet.
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#include "fastjet/GhostedAreaSpec.hh"
#include<iostream>
#include<sstream>

using namespace std;

FASTJET_BEGIN_NAMESPACE      // defined in fastjet/internal/base.hh

BasicRandom<double> GhostedAreaSpec::_random_generator;

//======================================================================
/// sets the detailed parameters for the ghosts (which may not be quite
/// the same as those requested -- this is in order for things to fit
/// in nicely into 2pi etc...
void GhostedAreaSpec::_initialize() {
  // add on area-measuring dummy particles
  _drap = sqrt(_ghost_area);
  _dphi = _drap;
  _nphi = int(ceil(twopi/_dphi)); _dphi = twopi/_nphi;
  _nrap = int(ceil(_ghost_maxrap/_drap)); _drap = _ghost_maxrap / _nrap;
  _actual_ghost_area = _dphi * _drap;
  _n_ghosts   = (2*_nrap+1)*_nphi;

  // checkpoint the status of the random number generator.
  checkpoint_random();
  //_random_generator.info(cerr);
}

//----------------------------------------------------------------------
/// adds the ghost 4-momenta to the vector of PseudoJet's
void GhostedAreaSpec::add_ghosts(vector<PseudoJet> & event) const {
  // add momenta for ghosts
  for (int irap = -_nrap; irap <= _nrap; irap++) {
    for (int iphi = 0; iphi < _nphi; iphi++) {
     
      // include random offsets for all quantities
      double phi = (iphi+0.5) * _dphi + _dphi*(_our_rand()-0.5)*_grid_scatter;
      double rap = irap * _drap + _drap*(_our_rand()-0.5)*_grid_scatter
                                                         + _ghost_rap_offset ;
      double kt = _mean_ghost_kt*(1+(_our_rand()-0.5)*_kt_scatter);

      double pminus = kt*exp(-rap);
      double pplus  = kt*exp(+rap);
      double px = kt*sin(phi);
      double py = kt*cos(phi);
      //cout << kt<<" "<<rap<<" "<<phi<<"\n";
      //if (phi>=twopi || phi < 0.0) cout << "Hey: "<< phi-twopi<<"\n";
      PseudoJet mom(px,py,0.5*(pplus-pminus),0.5*(pplus+pminus));
      event.push_back(mom);
    }
  }
}

string GhostedAreaSpec::description() const {

  ostringstream ostr;
  ostr << "ghosts of area " << actual_ghost_area() 
       << " (had requested " << ghost_area() << ")"
       << ", placed up to y = " << ghost_maxrap() 
       << ", scattered wrt to perfect grid by (rel) " << grid_scatter() 
       << ", mean_ghost_kt = " << mean_ghost_kt()
       << ", rel kt_scatter =  " << kt_scatter()
       << ", n repetitions of ghost distributions =  " << repeat();
  return ostr.str();
}

FASTJET_END_NAMESPACE