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UA5Handler.icc
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// -*- C++ -*-
//
// UA5Handler.icc is a part of Herwig++ - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2007 The Herwig Collaboration
//
// Herwig++ is licenced under version 2 of the GPL, see COPYING for details.
// Please respect the MCnet academic guidelines, see GUIDELINES for details.
//
//
// This is the implementation of the inlined member functions of
// the ForcedSplitting class.
//
namespace Herwig {
// This returns the mean multiplicity for the energy E amd the given parameters N1,N2,N3
inline double UA5Handler::meanMultiplicity(Energy E) const {
return _n1*pow(E/GeV,2.0*_n2)+_n3;
}
// This returns the randomly generated value for the negative binomial
inline double UA5Handler::negativeBinomial(int N, double mean, double ek) const {
if(N < 0) return 0.0;
double r = mean/ek;
double rval = pow(1.+r, -ek);
r /= (1.+r);
for(int i = 1; i<=N; i++) rval *= r*(ek+i-1.)/i;
return rval;
}
// This returns random number from dN/d(x**2)=exp(-B*TM) distribution, where
// TM = SQRT(X**2+AM0**2). Uses Newton's method to solve F-R=0
inline Energy UA5Handler::randExt(Energy AM0, InvEnergy B) const {
double r = rnd();
// Starting value
Energy am = AM0-log(r)/B;
for(int i = 1; i<20; ++i) {
double a = exp(-B*(am-AM0))/(1.+B*AM0);
double f = (1.+B*am)*a-r;
InvEnergy df = -B*B*am*a;
Energy dam = -f/df;
am += dam;
if(am<AM0) am = AM0 + .001*MeV;
if(abs(dam) < .001*MeV) break;
}
return am;
}
template <typename T>
inline T UA5Handler::gaussDistribution(T mean, T stdev) const {
double x = rnd();
x = sqrt(-2.*log(x));
double y;
randAzm(x,x,y);
return mean + stdev*x;
}
// This returns a random number with a flat distribution [-A,A] plus gaussian
// tail with stdev B
inline double UA5Handler::randUng(double A, double B) const {
double prun;
if(A == 0.) prun = 0.;
else prun = 1./(1.+B*1.2533/A);
if(rnd() < prun) return 2.*(rnd()-0.5)*A;
else {
double temp = gaussDistribution(0.,B);
if(temp < 0) return temp - abs(A);
else return temp + abs(A);
}
}
// Generates a random azimuthal angle and creates a 2 vector of length x with angle phi
template <typename T>
inline void UA5Handler::randAzm (T x, T &px, T &py) const {
double c,s,cs;
while(true) {
c = 2.*rnd()-1.;
s = 2.*rnd()-1.;
cs = c*c+s*s;
if(cs <= 1.&&cs!=0.) break;
}
T qt = x/cs;
px = (c*c-s*s)*qt;
py = 2.*c*s*qt;
}
}

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