G4LegendrePolynomial Class Reference

#include <G4LegendrePolynomial.hh>

Public Member Functions
G4double	EvalAssocLegendrePoly (G4int l, G4int m, G4double x, std::map< G4int, std::map< G4int, G4double > > *cache=NULL)
G4double	EvalLegendrePoly (G4int order, G4double x)
G4double	GetCoefficient (size_t i, size_t order)

Static Public Member Functions
static size_t	GetNCoefficients (size_t order)

Protected Member Functions
void	BuildUpToOrder (size_t order)

Protected Attributes
std::vector< std::vector< G4double > >	fCoefficients

Detailed Description

Definition at line 50 of file G4LegendrePolynomial.hh.

Member Function Documentation

BuildUpToOrder()

void G4LegendrePolynomial::BuildUpToOrder ( size_t  order )

protected

Definition at line 123 of file G4LegendrePolynomial.cc.

{
  if(orderMax > 30) {
    G4cout << "G4LegendrePolynomial::GetCoefficient(): "
           << "I refuse to make a Legendre Polynomial of order " 
           << orderMax << G4endl;
    return;
  }
  while(fCoefficients.size() < orderMax+1) {  /* Loop checking, 30-Oct-2015, G.Folger */
    size_t order = fCoefficients.size();
    fCoefficients.resize(order+1);
    if(order <= 1) fCoefficients[order].push_back(1.);
    else {
      for(size_t iCoeff = 0; iCoeff < order+1; ++iCoeff) {
        if((order % 2) == (iCoeff % 2)) {
          G4double coeff = 0;
          if(iCoeff <= order-2) coeff -= fCoefficients[order-2][iCoeff/2]*G4double(order-1);
          if(iCoeff > 0) coeff += fCoefficients[order-1][(iCoeff-1)/2]*G4double(2*order-1);
          coeff /= G4double(order);
          fCoefficients[order].push_back(coeff);
        }
      }
    }
  }
}

References fCoefficients, G4cout, and G4endl.

Referenced by GetCoefficient().

EvalAssocLegendrePoly()

G4double G4LegendrePolynomial::EvalAssocLegendrePoly	(	G4int	l,
		G4int	m,
		G4double	x,
		std::map< G4int, std::map< G4int, G4double > > *	cache = NULL
	)

Definition at line 49 of file G4LegendrePolynomial.cc.

{
  // Calculate P_l^m(x).
  // If cache ptr is non-null, use cache[l][m] if it exists, otherwise compute
  // P_l^m(x) and cache it in that position. The cache speeds up calculations
  // where many P_l^m computations are need at the same value of x.
 
  if(l<0 || m<-l || m>l) return 0;
  G4Pow* g4pow =  G4Pow::GetInstance();
 
  // Use non-log factorial for low l, m: it is more efficient until 
  // l and m get above 10 or so.
  // FIXME: G4Pow doesn't check whether the argument gets too large, 
  // which is unsafe! Max is 512; VI: It is assume that Geant4 does not
  // need higher order
  if(m<0) {
    G4double value = (m%2 ? -1. : 1.) * EvalAssocLegendrePoly(l, -m, x);
    if(l < 10) return value * g4pow->factorial(l+m)/g4pow->factorial(l-m);
    else { return value * G4Exp(g4pow->logfactorial(l+m) - g4pow->logfactorial(l-m));
    }
  }
 
  // hard-code the first few orders for speed
  if(l==0)   return 1;
  if(l==1) {
    if(m==0){return x;}
    /*m==1*/ return -sqrt(1.-x*x);
  }
  if(l<5) {
    G4double x2 = x*x;
    if(l==2) {
      if(m==0){return 0.5*(3.*x2 - 1.);}
      if(m==1){return -3.*x*sqrt(1.-x2);}
      /*m==2*/ return 3.*(1.-x2);
    }
    if(l==3) {
      if(m==0){return 0.5*(5.*x*x2 - 3.*x);}
      if(m==1){return -1.5*(5.*x2-1.)*sqrt(1.-x2);}
      if(m==2){return 15.*x*(1.-x2);}
      /*m==3*/ return -15.*(1.-x2)*sqrt(1.-x2);
    }
    if(l==4) {
      if(m==0){return 0.125*(35.*x2*x2 - 30.*x2 + 3.);}
      if(m==1){return -2.5*(7.*x*x2-3.*x)*sqrt(1.-x2);}
      if(m==2){return 7.5*(7.*x2-1.)*(1.-x2);}
      if(m==3){return -105.*x*(1.-x2)*sqrt(1.-x2);}
      /*m==4*/ return 105.*(1. - 2.*x2 + x2*x2);
    }
  }
 
  // Easy special cases
  // FIXME: G4Pow doesn't check whether the argument gets too large, which is unsafe! Max is 512. 
  if(m==l) return (l%2 ? -1. : 1.) * 
         G4Exp(g4pow->logfactorial(2*l) - g4pow->logfactorial(l)) * 
         G4Exp(G4Log((1.-x*x)*0.25)*0.5*G4double(l));
  if(m==l-1) return x*(2.*G4double(m)+1.)*EvalAssocLegendrePoly(m,m,x);
 
  // See if we have this value cached.
  if(cache != NULL && cache->count(l) > 0 && (*cache)[l].count(m) > 0) {
    return (*cache)[l][m];
  }
 
  // Otherwise calculate recursively
  G4double value = (x*G4double(2*l-1)*EvalAssocLegendrePoly(l-1,m,x) - 
               (G4double(l+m-1))*EvalAssocLegendrePoly(l-2,m,x))/G4double(l-m);
 
  // If we are working with a cache, cache this value.
  if(cache != NULL) {
    (*cache)[l][m] = value;
  }
  return value;
}

References EvalAssocLegendrePoly(), G4Pow::factorial(), G4Exp(), G4Log(), G4Pow::GetInstance(), G4Pow::logfactorial(), and m.

Referenced by EvalAssocLegendrePoly(), EvalLegendrePoly(), G4PolarizationTransition::GenerateGammaPhi(), and G4PolarizationTransition::SampleGammaTransition().

EvalLegendrePoly()

G4double G4LegendrePolynomial::EvalLegendrePoly	(	G4int	order,
		G4double	x
	)

Definition at line 43 of file G4LegendrePolynomial.cc.

{
  // Call EvalAssocLegendrePoly with m=0
  return (EvalAssocLegendrePoly(order,0,x));
}

References EvalAssocLegendrePoly().

GetCoefficient()

G4double G4LegendrePolynomial::GetCoefficient	(	size_t	i,
		size_t	order
	)

Definition at line 34 of file G4LegendrePolynomial.cc.

{
  if(order >= fCoefficients.size()) BuildUpToOrder(order);
  if(order >= fCoefficients.size() ||
     i/2 >= fCoefficients[order].size() ||
     (i%2) != order %2) return 0;
  return fCoefficients[order][i/2];
}

References BuildUpToOrder(), and fCoefficients.

Referenced by G4PolarizationTransition::GenerateGammaCosTheta().

GetNCoefficients()

static size_t G4LegendrePolynomial::GetNCoefficients ( size_t  order )

inlinestatic

Definition at line 54 of file G4LegendrePolynomial.hh.

{ return order+1; }

Referenced by G4PolarizationTransition::GenerateGammaCosTheta().

Field Documentation

fCoefficients

std::vector< std::vector<G4double> > G4LegendrePolynomial::fCoefficients

protected

Definition at line 64 of file G4LegendrePolynomial.hh.

Referenced by BuildUpToOrder(), and GetCoefficient().

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The documentation for this class was generated from the following files:

• source/processes/hadronic/util/include/G4LegendrePolynomial.hh
• source/processes/hadronic/util/src/G4LegendrePolynomial.cc