LHAPDF  6.5.4
Reweighting.h
1 // -*- C++ -*-
2 //
3 // This file is part of LHAPDF
4 // Copyright (C) 2012-2023 The LHAPDF collaboration (see AUTHORS for details)
5 //
6 #pragma once
7 #ifndef LHAPDF_Reweighting_H
8 #define LHAPDF_Reweighting_H
9 
10 #include "LHAPDF/PDF.h"
11 #include "LHAPDF/PDFSet.h"
12 
13 namespace LHAPDF {
14 
15 
18 
19  namespace {
20  inline bool _checkAlphasQ2(double Q2, const PDF& pdfa, const PDF& pdfb, double aschk) {
21  if (aschk < 0) return true;
22  const double as_a = pdfa.alphasQ2(Q2);
23  const double as_b = pdfb.alphasQ2(Q2);
24  if (2 * std::abs(as_a - as_b) / (std::abs(as_a) + std::abs(as_b)) < aschk) return true;
25  std::cerr << "WARNING: alpha_s(Q2) mismatch in PDF reweighting "
26  << "at Q2 = " << Q2 << " GeV2:\n "
27  << as_a << " for " << pdfa.set().name() << "/" << pdfa.memberID() << " vs. "
28  << as_b << " for " << pdfb.set().name() << "/" << pdfb.memberID()
29  << std::endl;
30  return false;
31  }
32  }
33 
34 
37 
41  inline double weightxQ2(int id, double x, double Q2, const PDF& basepdf, const PDF& newpdf, double aschk=5e-2) {
42  if (aschk >= 0) _checkAlphasQ2(Q2, basepdf, newpdf, aschk);
43  const double xf_base = basepdf.xfxQ2(id, x, Q2);
44  const double xf_new = newpdf.xfxQ2(id, x, Q2);
45  return xf_new / xf_base;
46  }
47 
51  template <typename PDFPTR>
52  inline double weightxQ2(int id, double x, double Q2, const PDFPTR basepdf, const PDFPTR newpdf, double aschk=5e-2) {
53  return weightxQ2(id, x, Q2, *basepdf, *newpdf, aschk);
54  }
55 
59  inline double weightxQ(int id, double x, double Q, const PDF& basepdf, const PDF& newpdf, double aschk=5e-2) {
60  return weightxQ2(id, x, sqr(Q), basepdf, newpdf, aschk);
61  }
62 
66  template <typename PDFPTR>
67  inline double weightxQ(int id, double x, double Q, const PDFPTR basepdf, const PDFPTR newpdf, double aschk=5e-2) {
68  return weightxQ(id, x, Q, *basepdf, *newpdf, aschk);
69  }
70 
72 
73 
76 
80  inline double weightxxQ2(int id1, int id2, double x1, double x2, double Q2, const PDF& basepdf, const PDF& newpdf, double aschk=5e-2) {
81  if (aschk >= 0) _checkAlphasQ2(Q2, basepdf, newpdf, aschk);
82  const double w1 = weightxQ2(id1, x1, Q2, basepdf, newpdf, -1);
83  const double w2 = weightxQ2(id2, x2, Q2, basepdf, newpdf, -1);
84  return w1 * w2;
85  }
86 
90  template <typename PDFPTR>
91  inline double weightxxQ2(int id1, int id2, double x1, double x2, double Q2, const PDFPTR basepdf, const PDFPTR newpdf, double aschk=5e-2) {
92  return weightxxQ2(id1, id2, x1, x2, Q2, *basepdf, *newpdf, aschk);
93  }
94 
98  inline double weightxxQ(int id1, int id2, double x1, double x2, double Q, const PDF& basepdf, const PDF& newpdf, double aschk=5e-2) {
99  return weightxxQ2(id1, id2, x1, x2, sqr(Q), basepdf, newpdf, aschk);
100  }
101 
105  template <typename PDFPTR>
106  inline double weightxxQ(int id1, int id2, double x1, double x2, double Q, const PDFPTR basepdf, const PDFPTR newpdf, double aschk=5e-2) {
107  return weightxxQ(id1, id2, x1, x2, Q, *basepdf, *newpdf, aschk);
108  }
109 
111 
113 
114 }
115 #endif
N sqr(const N &x)
Convenience function for squaring (of any type)
Definition: Utils.h:208
PDF is the general interface for access to parton density information.
Definition: PDF.h:40
double weightxxQ2(int id1, int id2, double x1, double x2, double Q2, const PDF &basepdf, const PDF &newpdf, double aschk=5e-2)
Definition: Reweighting.h:80
double weightxxQ(int id1, int id2, double x1, double x2, double Q, const PDF &basepdf, const PDF &newpdf, double aschk=5e-2)
Definition: Reweighting.h:98
double weightxQ(int id, double x, double Q, const PDF &basepdf, const PDF &newpdf, double aschk=5e-2)
Definition: Reweighting.h:59
double xfxQ2(int id, double x, double q2) const
Get the PDF xf(x) value at (x,q2) for the given PID.
Namespace for all LHAPDF functions and classes.
Definition: AlphaS.h:14
double weightxQ2(int id, double x, double Q2, const PDF &basepdf, const PDF &newpdf, double aschk=5e-2)
Definition: Reweighting.h:41