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//STARTHEADER
// $Id: Subtractor.cc 2577 2011-09-13 15:11:38Z salam $
//
// Copyright (c) 2005-2011, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
//
//----------------------------------------------------------------------
// This file is part of FastJet.
//
// FastJet is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// The algorithms that underlie FastJet have required considerable
// development and are described in hep-ph/0512210. If you use
// FastJet as part of work towards a scientific publication, please
// include a citation to the FastJet paper.
//
// FastJet is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with FastJet. If not, see <http://www.gnu.org/licenses/>.
//----------------------------------------------------------------------
//ENDHEADER
#include "fastjet/tools/Subtractor.hh"
#include <cassert>
#include <sstream>
#include <limits>
using namespace std;
FASTJET_BEGIN_NAMESPACE // defined in fastjet/internal/base.hh
const double Subtractor::_invalid_rho = -numeric_limits<double>::infinity();
Subtractor::Subtractor(double rho) : _bge(0), _rho(rho) {
assert(_rho>0.0);
}
PseudoJet Subtractor::result(const PseudoJet & jet) const {
if (!jet.has_area()){
throw Error("Trying to subtract a jet without area support");
}
double rho;
if (_bge != 0) {
rho = _bge->rho(jet);
} else if (_rho != _invalid_rho) {
rho = _rho;
} else {
throw Error("default Subtractor does not have any information about the background, which is needed to perform the subtraction");
}
PseudoJet subtracted_jet = jet;
PseudoJet area4vect = jet.area_4vector();
// sanity check
if (rho*area4vect.perp() < jet.perp() ) {
// this subtraction should retain the jet's structural
// information
subtracted_jet -= rho*area4vect;
} else {
// this sets the jet's momentum to zero while
// maintaining all of the jet's structural information
subtracted_jet *= 0;
}
return subtracted_jet;
}
//----------------------------------------------------------------------
std::string Subtractor::description() const{
if (_bge != 0) {
return "Subtractor that uses the following background estimator to determine rho: "+_bge->description();
} else if (_rho != _invalid_rho) {
ostringstream ostr;
ostr << "Subtractor that uses a fixed value of rho = " << _rho;
return ostr.str();
} else {
return "Uninitialised subtractor";
}
}
FASTJET_END_NAMESPACE
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