| Geant4 Cross Reference |
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25 //
26 //
27 // Abstract base class for multibody "phase space" generators. Subclasses
28 // implement a specific algorithm, such as Kopylov, GENBOD, or Makoto's
29 // NBody. Subclasses are used by G4HadPhaseSpaceGenerator.
30 //
31 // Author: Michael Kelsey (SLAC) <kelsey@slac.stanford.edu>
32
33 #include "G4VHadDecayAlgorithm.hh"
34 #include "G4HadronicException.hh"
35 #include "G4PhysicalConstants.hh"
36 #include "G4SystemOfUnits.hh"
37 #include "G4ThreeVector.hh"
38 #include "Randomize.hh"
39 #include <algorithm>
40 #include <iostream>
41 #include <iterator>
42 #include <numeric>
43 #include <vector>
44
45
46 // Initial state (rest mass) and list of final masses
47
48 void G4VHadDecayAlgorithm::Generate(G4double initialMass,
49 const std::vector<G4double>& masses,
50 std::vector<G4LorentzVector>& finalState) {
51 if (verboseLevel) G4cout << GetName() << "::Generate" << G4endl;
52
53 // Initialization and sanity check
54 finalState.clear();
55 if (!IsDecayAllowed(initialMass, masses)) return;
56
57 // Allow different procedures for two-body or N-body distributions
58 if (masses.size() == 2U)
59 GenerateTwoBody(initialMass, masses, finalState);
60 else
61 GenerateMultiBody(initialMass, masses, finalState);
62 }
63
64
65 // Base class does very simple validation of configuration
66
67 G4bool G4VHadDecayAlgorithm::
68 IsDecayAllowed(G4double initialMass,
69 const std::vector<G4double>& masses) const {
70 G4bool okay =
71 (initialMass > 0. && masses.size() >= 2 &&
72 initialMass >= std::accumulate(masses.begin(),masses.end(),0.));
73
74 if (verboseLevel) {
75 G4cout << GetName() << "::IsDecayAllowed? initialMass " << initialMass
76 << " " << masses.size() << " masses sum "
77 << std::accumulate(masses.begin(),masses.end(),0.) << G4endl;
78
79 if (verboseLevel>1) PrintVector(masses," ",G4cout);
80
81 G4cout << " Returning " << okay << G4endl;
82 }
83
84 return okay;
85 }
86
87
88 // Momentum function (c.f. PDK() function from CERNLIB W515)
89
90 G4double G4VHadDecayAlgorithm::TwoBodyMomentum(G4double M0, G4double M1,
91 G4double M2) const {
92 G4double PSQ = (M0+M1+M2)*(M0+M1-M2)*(M0-M1+M2)*(M0-M1-M2);
93 if (PSQ < 0.) {
94 G4cout << GetName() << ": problem of decay of M(GeV) " << M0/GeV
95 << " to M1(GeV) " << M1/GeV << " and M2(GeV) " << M2/GeV
96 << " PSQ(MeV) " << PSQ/MeV << " < 0" << G4endl;
97 // exception only if the problem is numerically significant
98 if (PSQ < -CLHEP::eV) {
99 throw G4HadronicException(__FILE__, __LINE__,"Error in decay kinematics");
100 }
101
102 PSQ = 0.;
103 }
104
105 return std::sqrt(PSQ)/(2.*M0);
106 }
107
108 // Convenience functions for uniform angular distributions
109
110 G4double G4VHadDecayAlgorithm::UniformTheta() const {
111 return std::acos(2.0*G4UniformRand() - 1.0);
112 }
113
114 G4double G4VHadDecayAlgorithm::UniformPhi() const {
115 return twopi*G4UniformRand();
116 }
117
118
119 // Dump contents of vector to output
120
121 void G4VHadDecayAlgorithm::
122 PrintVector(const std::vector<G4double>& v,
123 const G4String& vname, std::ostream& os) const {
124 os << " " << vname << "(" << v.size() << ") ";
125 std::copy(v.begin(), v.end(), std::ostream_iterator<G4double>(os, " "));
126 os << std::endl;
127 }
128