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25 //
26 // G4ILawTruncatedExp
27 // --------------------------------------------------------------------
28
29 #include "G4ILawTruncatedExp.hh"
30 #include "Randomize.hh"
31 #include "G4Track.hh"
32
33
34 G4ILawTruncatedExp::G4ILawTruncatedExp(const G4String& name)
35 : G4VBiasingInteractionLaw(name)
36 {}
37
38 G4ILawTruncatedExp::~G4ILawTruncatedExp()
39 {}
40
41 void G4ILawTruncatedExp::SetForceCrossSection(G4double crossSection)
42 {
43 if (crossSection < 0.0)
44 {
45 G4Exception("G4ILawTruncatedExp::SetForceCrossSection(..)",
46 "BIAS.GEN.09", JustWarning,
47 "Cross-section value passed is negative. It is set to zero !");
48 fIsSingular = true;
49 crossSection = 0.0;
50 }
51 fIsSingular = false;
52 fCrossSectionDefined = true;
53 fCrossSection = crossSection;
54 }
55
56 G4double G4ILawTruncatedExp::
57 ComputeEffectiveCrossSectionAt(G4double distance) const
58 {
59 if ( !fCrossSectionDefined )
60 {
61 G4Exception("G4ILawTruncatedExp::ComputeEffectiveCrossSection(..)",
62 "BIAS.GEN.10", JustWarning,
63 "Cross-section value requested, but has not been defined yet. Assumes 0 !");
64 // -- zero cross-section, returns the limit form of the effective cross-section:
65 return 1.0 / ( fMaximumDistance - distance );
66 }
67
68 G4double denum = 1.0 - std::exp(-fCrossSection *(fMaximumDistance-distance));
69 return fCrossSection/denum;
70 }
71
72 G4double G4ILawTruncatedExp::
73 ComputeNonInteractionProbabilityAt(G4double distance) const
74 {
75 if (!fCrossSectionDefined)
76 {
77 G4Exception("G4ILawTruncatedExp::ComputeNonInteractionProbability(..)",
78 "BIAS.GEN.11", JustWarning,
79 "Non interaction probability value requested, but cross section has not been defined yet. Assumes it to be 0 !");
80 // -- return limit case of null cross-section:
81 return 1.0 - distance / fMaximumDistance;
82 }
83 G4double num = 1.0 - std::exp( -fCrossSection*distance );
84 G4double denum = 1.0 - std::exp( -fCrossSection*fMaximumDistance );
85 return 1.0 - num/denum;
86 }
87
88 G4double G4ILawTruncatedExp::SampleInteractionLength()
89 {
90 if ( !fCrossSectionDefined )
91 {
92 G4Exception("G4ILawTruncatedExp::Sample(..)",
93 "BIAS.GEN.12", JustWarning,
94 "Trying to sample while cross-section is not defined, assuming 0 !");
95 fInteractionDistance = G4UniformRand() * fMaximumDistance;
96 return fInteractionDistance;
97 }
98 fInteractionDistance = -std::log(1.0-G4UniformRand()*(1.0-std::exp(-fCrossSection*fMaximumDistance)))/fCrossSection;
99 return fInteractionDistance;
100 }
101
102 G4double G4ILawTruncatedExp::
103 UpdateInteractionLengthForStep(G4double truePathLength)
104 {
105 fInteractionDistance -= truePathLength;
106 fMaximumDistance -= truePathLength;
107
108 if ( fInteractionDistance < 0 )
109 {
110 G4ExceptionDescription ed;
111 ed << " Negative number of interaction length for `" << GetName()
112 << "' " << fInteractionDistance << ", set it to zero !" << G4endl;
113 G4Exception("G4ILawTruncatedExp::UpdateInteractionLengthForStep(...)",
114 "BIAS.GEN.13", JustWarning,
115 "Trying to sample while cross-section is not defined, assuming 0 !");
116 fInteractionDistance = 0.;
117 }
118
119 return fInteractionDistance;
120 }
121