main54
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// main54.cc is a part of the PYTHIA event generator.
// Copyright (C) 2021 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;
}