G4Bessel.cc

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//
// %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
//
// MODULE:      G4Bessel.cc
//
// Version:     B.1
// Date:        15/04/04
// Author:      P R Truscott
// Organisation:    QinetiQ Ltd, UK
// Customer:        ESA/ESTEC, NOORDWIJK
// Contract:        17191/03/NL/LvH
//
// %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
//
// CHANGE HISTORY
// --------------
//
// 18 Noevmber 2003, P R Truscott, QinetiQ Ltd, UK
// Created.
//
// 15 March 2004, P R Truscott, QinetiQ Ltd, UK
// Beta release
//
// %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
//
#include "G4Bessel.hh"
#include "G4PhysicalConstants.hh"
//
G4Bessel::G4Bessel ()
{;}
//
G4Bessel::~G4Bessel ()
{;}
//
G4double G4Bessel::I0 (G4double x)
{
  const G4double P1 = 1.0,
                 P2 = 3.5156229,
                 P3 = 3.0899424,
                 P4 = 1.2067492,
                 P5 = 0.2659732,
                 P6 = 0.0360768,
                 P7 = 0.0045813;
  const G4double Q1 = 0.39894228,
                 Q2 = 0.01328592,
                 Q3 = 0.00225319,
                 Q4 =-0.00157565,
                 Q5 = 0.00916281,
                 Q6 =-0.02057706,
                 Q7 = 0.02635537,
                 Q8 =-0.01647633,
                 Q9 = 0.00392377;
  
  G4double I = 0.0;
  if (std::fabs(x) < 3.75)
  {
    G4double y = std::pow(x/3.75, 2.0);
    I = P1+y*(P2+y*(P3+y*(P4+y*(P5+y*(P6+y*P7)))));
  }
  else
  {
    G4double ax = std::fabs(x);
    G4double y  = 3.75/ax;
    I  = std::exp(ax) / std::sqrt(ax) *
      (Q1+y*(Q2+y*(Q3+y*(Q4+y*(Q5+y*(Q6+y*(Q7+y*(Q8+y*Q9))))))));
  }
  return I;
}
//
G4double G4Bessel::K0 (G4double x)
{
  const G4double P1 =-0.57721566,
                 P2 = 0.42278420,
                 P3 = 0.23069756,
                 P4 = 0.03488590,
                 P5 = 0.00262698,
                 P6 = 0.00010750,
                 P7 = 0.00000740;
  const G4double Q1 = 1.25331414,
                 Q2 =-0.07832358,
                 Q3 = 0.02189568,
                 Q4 =-0.01062446,
                 Q5 = 0.00587872,
                 Q6 =-0.00251540,
                 Q7 = 0.00053208;

  G4double K = 0.0;
  if (x <= 2.0)
  {
    G4double y = x * x / 4.0;
    K = (-std::log(x/2.0)) * I0(x) +
      P1+y*(P2+y*(P3+y*(P4+y*(P5+y*(P6+y*P7)))));
  }
  else
  {
    G4double y = 2.0 / x;
    K = std::exp(-x)  / std::sqrt(x) *
      (Q1+y*(Q2+y*(Q3+y*(Q4+y*(Q5+y*(Q6+y*Q7))))));
  }
  return K;
}
//
G4double G4Bessel::I1 (G4double x)
{
  const G4double P1 = 0.5,
                 P2 = 0.87890594,
                 P3 = 0.51498869,
                 P4 = 0.15084934,
                 P5 = 0.02658733,
                 P6 = 0.00301532,
                 P7 = 0.00032411;
  const G4double Q1 = 0.39894228,
                 Q2 =-0.03988024,
                 Q3 =-0.00362018,
                 Q4 = 0.00163801,
                 Q5 =-0.01031555,
                 Q6 = 0.02282967,
                 Q7 =-0.02895312,
                 Q8 = 0.01787654,
                 Q9 =-0.00420059;

  G4double I = 0.0;
  if (std::fabs(x) < 3.75)
  {
    G4double ax = std::fabs(x);
    G4double y = std::pow(x/3.75, 2.0);
    I = ax*(P1+y*(P2+y*(P3+y*(P4+y*(P5+y*(P6+y*P7))))));
  }
  else
  {
    G4double ax = std::fabs(x);
    G4double y  = 3.75/ax;
    I  = std::exp(ax) / std::sqrt(ax) *
      (Q1+y*(Q2+y*(Q3+y*(Q4+y*(Q5+y*(Q6+y*(Q7+y*(Q8+y*Q9))))))));
  }
  if (x < 0.0) I = -I;
  return I;
}
//
G4double G4Bessel::K1 (G4double x)
{
  const G4double P1 = 1.0,
                 P2 = 0.15443144,
                 P3 =-0.67278579,
                 P4 =-0.18156897,
                 P5 =-0.01919402,
                 P6 =-0.00110404,
                 P7 =-0.00004686;
  const G4double Q1 = 1.25331414,
                 Q2 = 0.23498619,
                 Q3 =-0.03655620,
                 Q4 = 0.01504268,
                 Q5 =-0.00780353,
                 Q6 = 0.00325614,
                 Q7 =-0.00068245;

  G4double K = 0.0;
  if (x <= 2.0)
  {
    G4double y = x * x / 4.0;
    K = std::log(x/2.0)*I1(x) + 1.0/x *
      (P1+y*(P2+y*(P3+y*(P4+y*(P5+y*(P6+y*P7))))));
  }
  else
  {
    G4double y = 2.0 / x;
    K = std::exp(-x) / std::sqrt(x) *
      (Q1+y*(Q2+y*(Q3+y*(Q4+y*(Q5+y*(Q6+y*Q7))))));
  }
  return K;
}
//
G4double G4Bessel::pI0 (G4double x)
{
  const G4double A0  = 0.1250000000000E+00,
                 A1  = 7.0312500000000E-02,
                 A2  = 7.3242187500000E-02,
                 A3  = 1.1215209960938E-01,
                 A4  = 2.2710800170898E-01,
                 A5  = 5.7250142097473E-01,
                 A6  = 1.7277275025845E+00,
                 A7  = 6.0740420012735E+00,
                 A8  = 2.4380529699556E+01,
                 A9  = 1.1001714026925E+02,
                 A10 = 5.5133589612202E+02,
                 A11 = 3.0380905109224E+03;

  G4double I = 0.0;
  if (x == 0.0)
  {
    I = 1.0;
  }
  else if (x < 18.0)
  {
    I          = 1.0;
    G4double y = x * x;
    G4double q = 1.0;
    for (G4int i=1; i<101; i++)
    {
      q *= 0.25 * y / i / i;
      I += q;
      if (std::abs(q/I) < 1.0E-15) break;
    }
  }
  else
  {
    G4double y = 1.0 / x;
    I = std::exp(x) / std::sqrt(twopi*x) *
      (1.0 + y*(A0+y*(A1+y*(A2+y*(A3+y*(A4+y*(A5+y*(A6+y*(A7+y*(A8+y*(A9+y*(A10+y*A11))))))))))));
  }

  return I;
}
//
G4double G4Bessel::pI1 (G4double x)
{
  const G4double A0  = -0.3750000000000E+00,
                 A1  = -1.1718750000000E-01,
                 A2  = -1.0253906250000E-01,
                 A3  = -1.4419555664063E-01,
                 A4  = -2.775764465332E-01,
                 A5  = -6.7659258842468E-01,
                 A6  = -1.9935317337513E+00,
                 A7  = -6.8839142681099E+00,
                 A8  = -2.7248827311269E+01,
                 A9  = -1.2159789187654E+02,
                 A10 = -6.0384407670507E+02,
                 A11 = -3.3022722944809E+03;

  G4double I = 0.0;
  if (x == 0.0)
  {
    I = 0.0;
  }
  else if (x < 18.0)
  {
    I          = 1.0;
    G4double y = x * x;
    G4double q = 1.0;
    for (G4int i=1; i<101; i++)
    {
      q *= 0.25 * y / i / (i+1.0);
      I += q;
      if (std::abs(q/I) < 1.0E-15) break;
    }
    I *= 0.5 * x;
    
  }
  else
  {
    G4double y = 1.0 / x;
    I = std::exp(x) / std::sqrt(twopi*x) *
      (1.0 + y*(A0+y*(A1+y*(A2+y*(A3+y*(A4+y*(A5+y*(A6+y*(A7+y*(A8+y*(A9+y*(A10+y*A11))))))))))));
  }

  return I;
}
//
G4double G4Bessel::pK0 (G4double x)
{
  const G4double A0 = 0.1250000000000E+00,
                 A1 = 0.2109375000000E+00,
                 A2 = 1.0986328125000E+00,
                 A3 = 1.1775970458984E+01,
                 A4 = 2.1461706161499E+02,
                 A5 = 5.9511522710323E+03,
                 A6 = 2.3347645606175E+05,
                 A7 = 1.2312234987631E+07;

  G4double K = 0.0;
  if (x == 0.0)
  {
    K = 1.0E+307;
  }
  else if (x < 9.0)
  {
    G4double y = x * x;
    G4double C = -std::log(x/2.0) - 0.5772156649015329;
    G4double q = 1.0;
    G4double t = 0.0;
    for (G4int i=1; i<51; i++)
    {
      q *= 0.25 * y / i / i;
      t += 1.0 / i ;
      K += q * (t+C);
    }
    K += C;
  }
  else
  {
    G4double y = 1.0 / x / x;
    K = 0.5 / x / pI0(x) *
      (1.0 + y*(A0+y*(A1+y*(A2+y*(A3+y*(A4+y*(A5+y*(A6+y*A7))))))));
  }
  
  return K;
}
//
G4double G4Bessel::pK1 (G4double x)
{
  G4double K = 0.0;
  if (x == 0.0)
    K = 1.0E+307;
  else
    K = (1.0/x - pI1(x)*pK0(x)) / pI0(x);
  return K;
}
//