main54

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// main54.cc is a part of the PYTHIA event generator.
// Copyright (C) 2020 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.

// Authors:
//            Juan Rojo

// Keywords:
//            Parton distribution
//            LHAPDF

// This program compares the internal and LHAPDF implementations of the
// NNPDF 2.3 QCD+QED sets, for results and for timing.
// Warning: this example is constructed to work for LHAPDF5.
// There seem to be differences when instead comparing with LHAPDF6.

#include "Pythia8/Pythia.h"
using namespace Pythia8;

int main() {

  cout<<"\n NNPDF2.3 QED LO phenomenology \n "<::infinity();
          cout << scientific << xlha[ix] << " " << a << " " << b
               << " " << diff << endl;
        }
      }
    }

    // Check photon.
    cout << "\n Now checking the photon PDF \n" << endl;
    for (int iq = 0; iq < iqMax; iq++) {
      cout << "  " << "x*gamma" << ", Q2 = " << Q2[iq] << endl;
      cout << "   x \t     Pythia8\t   LHAPDF\t   diff(%) " << endl;
      for (int ix = 0; ix < 2; ix++) {
        double a = pdfs_nnpdf.xf( 22, xlha[ix], Q2[iq]);
        double b = pdfs_nnpdf_lha.xf( 22, xlha[ix], Q2[iq]);
        double diff = b != 0 ? 1e2 * abs((a-b)/b) :
          std::numeric_limits::infinity();
        cout << scientific << xlha[ix] << " " << a << " " << b
             << " " << diff << endl;
      }
    }

    // Now check the timings for evolution.
    cout << "\n Checking timings " << endl;

    clock_t t1 = clock();
    for (int f = -4; f < 4; f++) {
      for (int iq = 0; iq < nq; iq++) {
        double qq2 = 2.0 * pow( 1e6 / 2.0, double(iq)/nq);
        for (int ix = 0; ix < nx; ix++) {
          double xx = 1e-6 * pow( 9e-1 / 1e-6, double(ix)/nx);
          pdfs_nnpdf.xf(f,xx,qq2);
        }
      }
    }
    clock_t t2 = clock();
    cout << " NNPDF internal timing = " << (t2-t1)/(double)CLOCKS_PER_SEC
         << endl;

    t1=clock();
    for (int f = -4; f < 4; f++) {
      for (int iq = 0; iq < nq; iq++) {
        double qq2 = 2.0 * pow(1e6 / 2.0, double(iq)/nq);
        for (int ix = 0; ix < nx; ix++) {
          double xx = 1e-6 * pow( 9e-1 / 1e-6, double(ix)/nx);
          pdfs_nnpdf_lha.xf(f,xx,qq2);
        }
      }
    }
    t2=clock();
    cout << " NNPDF LHAPDF   timing = " << (t2-t1)/(double)CLOCKS_PER_SEC
         << endl;

  } // End loop over NNPDF internal sets

  // Done.
  cout << "\n Compared LHAPDF and internal Pythia8 results.\n" << endl;

  return 0;
}