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// #############################################
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// Note : this is a snippet to re-weighting pdf.
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// Not a stand along code
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// #############################################
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PDFAnalyzer::PDFAnalyzer(const edm::ParameterSet& iConfig)
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{
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/// Parameters:
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pdfInfoTag = iConfig.getUntrackedParameter<edm::InputTag> ("PdfInfoTag", edm::InputTag("genEventPdfInfo"));
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pdfSetName = iConfig.getUntrackedParameter<std::string> ("PdfSetName", "cteq65");
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// Force unsetting of the LHAPATH variable to avoid potential problems
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gSystem->Setenv("LHAPATH","<Your Local LHAPDFLIB Dir>/share/lhapdf/PDFsets/");
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//gSystem->Setenv("LHAPATH","/uscmst1/prod/sw/cms/slc5_ia32_gcc434/external/lhapdf/5.6.0-cms2/share/lhapdf/PDFsets/");
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//gSystem->Setenv("LHAPATH","/afs/cern.ch/cms/sw/slc4_ia32_gcc345/external/lhapdf/5.6.0-cms/share/lhapdf/PDFsets/");
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LHAPDF::setVerbosity(LHAPDF::SILENT);
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LHAPDF::initPDFSet(pdfSetName, LHAPDF::LHGRID, 0); // Type: LHGRID(preferred) or LHPDF
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LHAPDF::getDescription();
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nmembers = LHAPDF::numberPDF() + 1;
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}
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// ....
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void
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PDFAnalyzer::analyze(const edm::Event& iEvent, const edm::EventSetup& iSetup)
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{
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// Get the collection
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edm::Handle<reco::PdfInfo> pdfstuff;
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bool runPDF = false;
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if ((!iEvent.isRealData()) && iEvent.getByLabel(pdfInfoTag, pdfstuff))
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runPDF = true;
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// Reweighting
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std::vector<double> weights;
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if (debug) std::cout<<"runPDF before Top Reconstruction = "<<runPDF<<std::endl;
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if(runPDF){
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float Q = pdfstuff->scalePDF;
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int id1 = (int)pdfstuff->id1;
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double x1 = pdfstuff->x1;
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double pdf1 = pdfstuff->pdf1;
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int id2 = (int)pdfstuff->id2;
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double x2 = pdfstuff->x2;
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double pdf2 = pdfstuff->pdf2;
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if(debug){
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std::cout<<"Q = "<<Q<<std::endl;
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std::cout<<"(id1,x1,pdf1) = "<<id1<<","<<x1<<","<<pdf1<<std::endl;
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std::cout<<"(id2,x2,pdf2) = "<<id2<<","<<x2<<","<<pdf2<<std::endl;
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}
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if (pdf1 != 0 && pdf2 != 0){
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// Put PDF weights in the event
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weights.reserve(nmembers);
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for (unsigned int i=0; i<nmembers; ++i) {
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LHAPDF::usePDFMember(i);
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double newpdf1 = LHAPDF::xfx(x1, Q, id1)/x1;
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double newpdf2 = LHAPDF::xfx(x2, Q, id2)/x2;
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if(debug){
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std::cout<<"newpdf1 = "<<newpdf1<<"; ";
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std::cout<<"newpdf2 = "<<newpdf2<<"; ";
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std::cout<<"weights["<<i<<"] = "<<newpdf1/pdf1*newpdf2/pdf2<<std::endl;
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}
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weights.push_back(newpdf1/pdf1*newpdf2/pdf2);
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}
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}else{
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std::cout<<"weights diverge, skip this event!"<<std::endl;
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runPDF = false;
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}
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}
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// Do your event selections
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// Example of how to apply the weight
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if (runPDF){
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for(int i=0; i < nmembers; i++){
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TString suffix = "PDF_";
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suffix+=i;
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double ww = weights[i]/weights[0];
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if(debug){
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std::cout<<"Weights = "<< ww <<"; ";
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std::cout<<TString("HadronicTop_mass_M3_")+suffix<<std::endl;
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}
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h1[TString("HadronicTop_mass_M3_")+suffix]->Fill(hadTopP4.M(),ww);
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}
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}
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}
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