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// $Id: G4InuclSpecialFunctions.cc,v 1.21 2010/09/14 17:51:36 mkelsey Exp $
// Geant4 tag: $Name: hadr-casc-V09-03-85 $
//
// 20100114  M. Kelsey -- Remove G4CascadeMomentum, use G4LorentzVector directly
// 20100914  M. Kelsey -- Migrate to integer A and Z.  Discard pointless
//		verbosity.

#include "G4InuclSpecialFunctions.hh"
#include "G4LorentzVector.hh"
#include "G4ThreeVector.hh"
#include "Randomize.hh"
#include <cmath>


G4double G4InuclSpecialFunctions::getAL(G4int A) {
  return 0.76 + 2.2 / G4cbrt(A);
}

G4double G4InuclSpecialFunctions::csNN(G4double e) {
  G4double snn;

  if (e < 40.0) {
    snn = -1174.8 / (e * e) + 3088.5 / e + 5.3107;
  } else {
    snn = 93074.0 / (e * e) - 11.148 / e + 22.429;
  }

  return snn; 
}

G4double G4InuclSpecialFunctions::csPN(G4double e) {
  G4double spn;

  if (e < 40.0) {
    spn = -5057.4 / (e * e) + 9069.2 / e + 6.9466;
  } else {
    spn = 239380.0 / (e * e) + 1802.0 / e + 27.147;
  }

  return spn; 
}

// calculates the nuclei Fermi energy for 0 - neutron and 1 - proton

G4double G4InuclSpecialFunctions::FermiEnergy(G4int A, G4int Z, G4int ntype) {
  const G4double C = 55.4;
  G4double arg = (ntype==0) ? G4double(A-Z)/A : G4double(Z)/A;

  return C * G4cbrt(arg*arg);	// 2/3 power
}

G4double G4InuclSpecialFunctions::G4cbrt(G4double x) {
  return x==0 ? 0. : (x<0?-1.:1.)*std::exp(std::log(std::fabs(x))/3.);
}

G4double G4InuclSpecialFunctions::inuclRndm() { 
  G4double rnd = G4UniformRand(); 
  return rnd;
} 

G4double G4InuclSpecialFunctions::randomGauss(G4double sigma) {
  const G4double eps = 1.0e-6;
  const G4double twopi = 6.2831854;
  G4double r1 = inuclRndm();
  r1 = r1 > eps ? r1 : eps;
  G4double r2 = inuclRndm();
  r2 = r2 > eps ? r2 : eps;
  r2 = r2 < 1.0 - eps ? r2 : 1.0 - eps; 

  return sigma * std::sin(twopi * r1) * std::sqrt(-2.0 * std::log(r2)); 
} 

G4double G4InuclSpecialFunctions::randomPHI() { 
  const G4double twopi = 6.2831853;
  return twopi * inuclRndm();
} 

std::pair<G4double, G4double> G4InuclSpecialFunctions::randomCOS_SIN() {
  G4double CT = 1.0 - 2.0 * inuclRndm();

  return std::pair<G4double, G4double>(CT, std::sqrt(1.0 - CT*CT));
}

G4LorentzVector 
G4InuclSpecialFunctions::generateWithFixedTheta(G4double ct, G4double p, 
						G4double m) {
  G4double phi = randomPHI();
  G4double pt = p * std::sqrt(std::fabs(1.0 - ct * ct));

  static G4ThreeVector pvec;	// Buffers to avoid memory thrashing
  static G4LorentzVector momr;

  pvec.set(pt*std::cos(phi), pt*std::sin(phi), p*ct);
  momr.setVectM(pvec, m);

  return momr;
}

G4LorentzVector 
G4InuclSpecialFunctions::generateWithRandomAngles(G4double p, G4double m) {
  std::pair<G4double, G4double> COS_SIN = randomCOS_SIN();
  G4double phi = randomPHI();
  G4double pt = p * COS_SIN.second;
  
  static G4ThreeVector pvec;	// Buffers to avoid memory thrashing
  static G4LorentzVector momr;

  pvec.set(pt*std::cos(phi), pt*std::sin(phi), p*COS_SIN.first);
  momr.setVectM(pvec, m);

  return momr;
}
