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G4EqGravityField.cc
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25 //
26 // G4EqGravityField implementation
27 //
28 // This is the right-hand side for equation of motion for a
29 // massive particle in a gravitational field.
30 //
31 // Created: P.Gumplinger, 14.06.11 - Adopted from G4EqMagElectricField
32 // Thanks to P.Fierlinger (PSI) and A.Capra and A.Fontana (INFN Pavia)
33 // -------------------------------------------------------------------
34 
35 #include "G4EqGravityField.hh"
36 #include "globals.hh"
37 #include "G4PhysicalConstants.hh"
38 
40  : G4EquationOfMotion( gField )
41 {
42 }
43 
45 {
46 }
47 
48 void
50  G4double,
51  G4double particleMass )
52 {
53  fMass = particleMass;
54 }
55 
56 void
58  const G4double G[],
59  G4double dydx[] ) const
60 {
61 
62  // Components of y:
63  // 0-2 dr/ds,
64  // 3-5 dp/ds - momentum derivatives
65 
66  G4double momentum_mag_square = y[3]*y[3] + y[4]*y[4] + y[5]*y[5];
67  G4double inv_momentum_magnitude = 1.0 / std::sqrt( momentum_mag_square );
68 
69  G4double Energy = std::sqrt(momentum_mag_square + fMass*fMass);
70  G4double cof2 = Energy/c_light;
71  G4double cof1 = inv_momentum_magnitude*fMass;
72  G4double inverse_velocity = Energy*inv_momentum_magnitude/c_light;
73 
74  dydx[0] = y[3]*inv_momentum_magnitude; // (d/ds)x = Vx/V
75  dydx[1] = y[4]*inv_momentum_magnitude; // (d/ds)y = Vy/V
76  dydx[2] = y[5]*inv_momentum_magnitude; // (d/ds)z = Vz/V
77 
78  dydx[3] = G[0]*cof1*cof2/c_light;
79  dydx[4] = G[1]*cof1*cof2/c_light; // m*g
80  dydx[5] = G[2]*cof1*cof2/c_light;
81 
82  // Lab Time of flight
83  //
84  dydx[7] = inverse_velocity;
85 
86  return;
87 }