MC_XS.cc

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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "HepMC/HepMCDefs.h"

namespace Rivet {

  /// @brief Analysis for the generated cross section
  class MC_XS : public Analysis {
  public:

    /// @name Constructors etc.
    //@{

    /// Constructor
    MC_XS()
      : Analysis("MC_XS")
    {    }

    //@}


  public:

    /// @name Analysis methods
    //@{

    /// Book histograms and initialise projections before the run
    void init() {
      /// @todo Convert to Scatter1D or Counter
      _h_XS   = bookScatter2D("XS");
      _h_N    = bookHisto1D("N", 1, 0.0, 1.0);
      _h_pmXS = bookHisto1D("pmXS", 2, -1.0, 1.0);
      _h_pmN  = bookHisto1D("pmN", 2, -1.0, 1.0);
      _mc_xs = _mc_error = 0.;
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      _h_N->fill(0.5,1.);
      _h_pmXS->fill(0.5*(event.weight() > 0 ? 1. : -1), abs(event.weight()));
      _h_pmN ->fill(0.5*(event.weight() > 0 ? 1. : -1), 1.);
      #ifdef HEPMC_HAS_CROSS_SECTION
      _mc_xs    = event.genEvent()->cross_section()->cross_section();
      _mc_error = event.genEvent()->cross_section()->cross_section_error();
      #endif
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_h_pmXS, crossSection()/sumOfWeights());
      #ifndef HEPMC_HAS_CROSS_SECTION
      _mc_xs = crossSection();
      _mc_error = 0.0;
      #endif
      _h_XS->addPoint(0, _mc_xs, 0.5, _mc_error);
    }

    //@}


  private:

    /// @name Histograms
    //@{
    Scatter2DPtr _h_XS;
    Histo1DPtr _h_N;
    Histo1DPtr _h_pmXS;
    Histo1DPtr _h_pmN;
    double _mc_xs, _mc_error;
    //@}

  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(MC_XS);

}