main86
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// main86.cc is a part of the PYTHIA event generator.
// Copyright (C) 2019 Torbjorn Sjostrand.
// PYTHIA is licenced under the GNU GPL v2 or later, see COPYING for details.
// Please respect the MCnet Guidelines, see GUIDELINES for details.
// Author: Stefan Prestel.
// Keywords: merging; leading order; UMEPS; hepmc;
// It illustrates how to do UMEPS merging, see the Matrix Element
// Merging page in the online manual. An example command is
// ./main86 main86.cmnd w_production hepmcout86.dat
// where main86.cmnd supplies the commands, w_production provides the
// input LHE events, and hepmcout86.dat is the output file. This
// example requires HepMC.
#include "Pythia8/Pythia.h"
#include "Pythia8Plugins/HepMC2.h"
#include
using namespace Pythia8;
//==========================================================================
// Example main programm to illustrate merging
int main( int argc, char* argv[] ){
// Check that correct number of command-line arguments
if (argc != 4) {
cerr << " Unexpected number of command-line arguments ("< xsecLO;
vector nAcceptLO;
cout << endl << endl << endl;
cout << "Start estimating umeps tree level cross section" << endl;
while(njetcounterLO >= 0) {
// From njet, choose LHE file
stringstream in;
in << "_" << njetcounterLO << ".lhe";
#ifdef GZIPSUPPORT
if(access( (iPathTree+in.str()+".gz").c_str(), F_OK) != -1) in << ".gz";
#endif
string LHEfile = iPathTree + in.str();
pythia.settings.mode("Merging:nRequested", njetcounterLO);
pythia.settings.mode("Beams:frameType", 4);
pythia.settings.word("Beams:LHEF", LHEfile);
pythia.init();
// Start generation loop
for( int iEvent=0; iEvent 0 )
njetcounterLO--;
else
break;
} // end loop over different jet multiplicities
// Switch off cross section estimation.
pythia.settings.flag("Merging:doXSectionEstimate", false);
// Switch showering and multiple interaction back on.
pythia.settings.flag("PartonLevel:FSR",fsr);
pythia.settings.flag("PartonLevel:ISR",isr);
pythia.settings.flag("HadronLevel:all",had);
pythia.settings.flag("PartonLevel:MPI",mpi);
// Declare sample cross section for output.
double sigmaTemp = 0.;
vector sampleXStree;
vector sampleXSsubtTree;
// Cross section an error.
double sigmaTotal = 0.;
double errorTotal = 0.;
int sizeLO = int(xsecLO.size());
njetcounterLO = nMaxLO;
iPathTree = iPath + "_tree";
while(njetcounterLO >= 0){
// From njet, choose LHE file
stringstream in;
in << "_" << njetcounterLO << ".lhe";
#ifdef GZIPSUPPORT
if(access( (iPathTree+in.str()+".gz").c_str(), F_OK) != -1) in << ".gz";
#endif
string LHEfile = iPathTree + in.str();
pythia.settings.flag("Merging:doUMEPSTree",true);
pythia.settings.flag("Merging:doUMEPSSubt",false);
pythia.settings.mode("Merging:nRecluster",0);
cout << endl << endl << endl
<< "Start tree level treatment for " << njetcounterLO << " jets"
<< endl;
pythia.settings.mode("Merging:nRequested", njetcounterLO);
pythia.settings.mode("Beams:frameType", 4);
pythia.settings.word("Beams:LHEF", LHEfile);
pythia.init();
// Remember position in vector of cross section estimates.
int iNow = sizeLO-1-njetcounterLO;
// Start generation loop
for( int iEvent=0; iEventweights().push_back(weight*normhepmc);
// Fill HepMC event.
ToHepMC.fill_next_event( pythia, hepmcevt );
// Add the weight of the current event to the cross section.
sigmaTotal += weight*normhepmc;
sigmaTemp += weight*normhepmc;
errorTotal += pow2(weight*normhepmc);
// Report cross section to hepmc
HepMC::GenCrossSection xsec;
xsec.set_cross_section( sigmaTotal*1e9, pythia.info.sigmaErr()*1e9 );
hepmcevt->set_cross_section( xsec );
// Write the HepMC event to file. Done with it.
ascii_io << hepmcevt;
delete hepmcevt;
} // end loop over events to generate
// print cross section, errors
pythia.stat();
// Save sample cross section for output.
sampleXStree.push_back(sigmaTemp);
sigmaTemp = 0.;
// Restart with ME of a reduced the number of jets
if( njetcounterLO > 0 )
njetcounterLO--;
else
break;
}
cout << endl << endl << endl;
cout << "Do UMEPS subtraction" << endl;
int njetcounterLS = nMaxLO;
string iPathSubt = iPath + "_tree";
while(njetcounterLS >= 1){
// From njet, choose LHE file
stringstream in;
in << "_" << njetcounterLS << ".lhe";
#ifdef GZIPSUPPORT
if(access( (iPathSubt+in.str()+".gz").c_str(), F_OK) != -1) in << ".gz";
#endif
string LHEfile = iPathSubt + in.str();
pythia.settings.flag("Merging:doUMEPSTree",false);
pythia.settings.flag("Merging:doUMEPSSubt",true);
pythia.settings.mode("Merging:nRecluster",1);
cout << endl << endl << endl
<< "Start subtractive treatment for " << njetcounterLS << " jets"
<< endl;
pythia.settings.mode("Merging:nRequested", njetcounterLS);
pythia.settings.mode("Beams:frameType", 4);
pythia.settings.word("Beams:LHEF", LHEfile);
pythia.init();
// Remember position in vector of cross section estimates.
int iNow = sizeLO-1-njetcounterLS;
// Start generation loop
for( int iEvent=0; iEventweights().push_back(weight*normhepmc);
// Fill HepMC event.
ToHepMC.fill_next_event( pythia, hepmcevt );
// Add the weight of the current event to the cross section.
sigmaTotal += weight*normhepmc;
sigmaTemp += weight*normhepmc;
errorTotal += pow2(weight*normhepmc);
// Report cross section to hepmc.
HepMC::GenCrossSection xsec;
xsec.set_cross_section( sigmaTotal*1e9, pythia.info.sigmaErr()*1e9 );
hepmcevt->set_cross_section( xsec );
// Write the HepMC event to file. Done with it.
ascii_io << hepmcevt;
delete hepmcevt;
} // end loop over events to generate
// print cross section, errors
pythia.stat();
// Save sample cross section for output.
sampleXSsubtTree.push_back(sigmaTemp);
sigmaTemp = 0.;
// Restart with ME of a reduced the number of jets
if( njetcounterLS > 1 )
njetcounterLS--;
else
break;
}
// Print cross section information.
cout << endl << endl;
cout << " *---------------------------------------------------*" << endl;
cout << " | |" << endl;
cout << " | Sample cross sections after UMEPS merging |" << endl;
cout << " | |" << endl;
cout << " | Leading order cross sections (mb): |" << endl;
for (int i = 0; i < int(sampleXStree.size()); ++i)
cout << " | " << sampleXStree.size()-1-i << "-jet: "
<< setw(17) << scientific << setprecision(6)
<< sampleXStree[i] << " |" << endl;
cout << " | |" << endl;
cout << " | Leading-order subtractive cross sections (mb): |" << endl;
for (int i = 0; i < int(sampleXSsubtTree.size()); ++i)
cout << " | " << sampleXSsubtTree.size()-1-i+1 << "-jet: "
<< setw(17) << scientific << setprecision(6)
<< sampleXSsubtTree[i] << " |" << endl;
cout << " | |" << endl;
cout << " |---------------------------------------------------|" << endl;
cout << " |---------------------------------------------------|" << endl;
cout << " | Inclusive cross sections: |" << endl;
cout << " | |" << endl;
cout << " | UMEPS merged inclusive cross section: |" << endl;
cout << " | " << setw(17) << scientific << setprecision(6)
<< sigmaTotal << " +- " << setw(17) << sqrt(errorTotal) << " mb "
<< " |" << endl;
cout << " | |" << endl;
cout << " | LO inclusive cross section: |" << endl;
cout << " | " << setw(17) << scientific << setprecision(6)
<< xsecLO.back() << " mb |" << endl;
cout << " | |" << endl;
cout << " *---------------------------------------------------*" << endl;
cout << endl << endl;
// Done
return 0;
}