Geant4  10.01.p03
CexmcReimplementedGenbod.cc
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26 /*
27  * =============================================================================
28  *
29  * Filename: CexmcReimplementedGenbod.cc
30  *
31  * Description: reimplemented GENBOD
32  * (mostly adopted from ROOT TGenPhaseSpace)
33  *
34  * Version: 1.0
35  * Created: 08.09.2010 18:52:39
36  * Revision: none
37  * Compiler: gcc
38  *
39  * Author: Alexey Radkov (),
40  * Company: PNPI
41  *
42  * =============================================================================
43  */
44 
45 #include <cmath>
46 #include <Randomize.hh>
47 #include <G4PhysicalConstants.hh>
48 #include <G4SystemOfUnits.hh>
50 #include "CexmcException.hh"
51 
52 
53 namespace
54 {
55  G4int DoubleMax( const void * a, const void * b )
56  {
57  G4double aa( *( ( G4double * )a ) );
58  G4double bb( *( ( G4double * )b ) );
59 
60  if ( aa > bb )
61  return 1;
62 
63  if ( aa < bb )
64  return -1;
65 
66  return 0;
67  }
68 
69 
70  G4double PDK( G4double a, G4double b, G4double c )
71  {
72  G4double x( ( a - b - c ) * ( a + b + c ) * ( a - b + c ) *
73  ( a + b - c ) );
74  x = std::sqrt( x ) / ( 2 * a );
75 
76  return x;
77  }
78 }
79 
80 
82  nmbOfOutputParticles( 0 )
83 {
84 }
85 
86 
88 {
89  // Generate a random final state.
90  // The function returns the weigth of the current event.
91  // Note that Momentum, Energy units are Gev/C, GeV
92 
93  G4double te_minus_tm( totalEnergy - totalMass );
94  G4double rno[ maxParticles ];
95  rno[ 0 ] = 0;
96 
97  if ( nmbOfOutputParticles > 2 )
98  {
99  for ( G4int i( 1 ); i < nmbOfOutputParticles - 1; ++i )
100  {
101  rno[ i ] = G4UniformRand();
102  }
103  qsort( rno + 1, nmbOfOutputParticles - 2, sizeof( G4double ),
104  DoubleMax );
105  }
106  rno[ nmbOfOutputParticles - 1 ] = 1;
107 
108  G4double invMas[ maxParticles ];
109  G4double sum( 0 );
110 
111  for ( int i( 0 ); i < nmbOfOutputParticles; ++i )
112  {
113  sum += outVec[ i ].mass / GeV;
114  invMas[ i ] = rno[ i ] * te_minus_tm / GeV + sum;
115  }
116 
117  //
118  //-----> compute the weight of the current event
119  //
120  G4double wt( maxWeight );
121  G4double pd[ maxParticles ];
122 
123  for ( int i( 0 ); i < nmbOfOutputParticles - 1; ++i )
124  {
125  pd[ i ] = PDK( invMas[ i + 1 ], invMas[ i ],
126  outVec[ i + 1 ].mass / GeV );
127  wt *= pd[ i ];
128  }
129 
130  //
131  //-----> complete specification of event (Raubold-Lynch method)
132  //
133  outVec[ 0 ].lVec->setPx( 0. );
134  outVec[ 0 ].lVec->setPy( pd[ 0 ] );
135  outVec[ 0 ].lVec->setPz( 0. );
136  outVec[ 0 ].lVec->setE( std::sqrt( pd[ 0 ] * pd[ 0 ] +
137  outVec[ 0 ].mass / GeV *
138  outVec[ 0 ].mass / GeV ) );
139 
140  G4int i( 1 );
141 
142  while ( true )
143  {
144  outVec[ i ].lVec->setPx( 0. );
145  outVec[ i ].lVec->setPy( -pd[ i - 1 ] );
146  outVec[ i ].lVec->setPz( 0. );
147  outVec[ i ].lVec->setE( std::sqrt( pd[ i - 1 ] * pd[ i - 1 ] +
148  outVec[ i ].mass / GeV *
149  outVec[ i ].mass / GeV ) );
150 
151  G4double cZ( 2 * G4UniformRand() - 1 );
152  G4double sZ( std::sqrt( 1 - cZ * cZ ) );
153  G4double angY( 2 * pi * G4UniformRand() );
154  G4double cY( std::cos( angY ) );
155  G4double sY( std::sin( angY ) );
156 
157  for ( int j( 0 ); j <= i; ++j )
158  {
159  G4LorentzVector * v( outVec[ j ].lVec );
160  G4double x( v->px() );
161  G4double y( v->py() );
162  v->setPx( cZ * x - sZ * y );
163  v->setPy( sZ * x + cZ * y ); // rotation around Z
164  x = v->px();
165  G4double z( v->pz() );
166  v->setPx( cY * x - sY * z );
167  v->setPz( sY * x + cY * z ); // rotation around Y
168  }
169 
170  if ( i == nmbOfOutputParticles - 1 )
171  break;
172 
173  G4double beta( pd[ i ] / std::sqrt( pd[ i ] * pd[ i ] +
174  invMas[ i ] * invMas[ i ] ) );
175  for ( int j( 0 ); j <= i; ++j )
176  outVec[ j ].lVec->boost( 0, beta, 0 );
177 
178  ++i;
179  }
180 
181  for ( int i( 0 ); i < nmbOfOutputParticles; ++i )
182  *outVec[ i ].lVec *= GeV;
183 
184  //
185  //---> return the weigth of event
186  //
187  return wt;
188 }
189 
190 
192 {
193  nmbOfOutputParticles = outVec.size();
194 
195  if ( nmbOfOutputParticles < 2 || nmbOfOutputParticles > maxParticles )
197 
198  SetMaxWeight();
199 }
200 
201 
203 {
204  SetMaxWeight();
205 }
206 
207 
209 {
210  G4double te_minus_tm( totalEnergy - totalMass );
211 
212  if ( fermiEnergyDepIsOn )
213  {
214  // ffq[] = pi * (2*pi)**(N-2) / (N-2)!
215  G4double ffq[] = { 0
216  ,3.141592, 19.73921, 62.01255, 129.8788, 204.0131
217  ,256.3704, 268.4705, 240.9780, 189.2637
218  ,132.1308, 83.0202, 47.4210, 24.8295
219  ,12.0006, 5.3858, 2.2560, 0.8859 };
220  maxWeight =
221  std::pow( te_minus_tm / GeV, nmbOfOutputParticles - 2 ) *
222  ffq[ nmbOfOutputParticles - 1 ] / ( totalEnergy / GeV );
223  }
224  else
225  {
226  G4double emmax( ( te_minus_tm + outVec[ 0 ].mass ) / GeV );
227  G4double emmin( 0. );
228  G4double wtmax( 1. );
229 
230  for ( G4int i( 1 ); i < nmbOfOutputParticles; ++i )
231  {
232  emmin += outVec[ i - 1 ].mass / GeV;
233  emmax += outVec[ i ].mass / GeV;
234  wtmax *= PDK( emmax, emmin, outVec[ i ].mass / GeV );
235  }
236  maxWeight = 1 / wtmax;
237  }
238 }
239 
G4double z
Definition: TRTMaterials.hh:39
const G4double pi
G4double a
Definition: TRTMaterials.hh:39
CexmcPhaseSpaceOutVector outVec
int G4int
Definition: G4Types.hh:78
static ulg bb
Definition: csz_inflate.cc:359
#define G4UniformRand()
Definition: Randomize.hh:93
static const double GeV
Definition: G4SIunits.hh:196
double G4double
Definition: G4Types.hh:76
CLHEP::HepLorentzVector G4LorentzVector