EvtdFunctionSingle.cc

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//--------------------------------------------------------------------------
//
// Environment:
//      This software is part of the EvtGen package developed jointly
//      for the BaBar and CLEO collaborations.  If you use all or part
//      of it, please give an appropriate acknowledgement.
//
// Copyright Information: See EvtGen/COPYRIGHT
//      Copyright (C) 2000      Caltech, UCSB
//
// Module: EvtdFunctionSingle.cc
//
// Description: Evaluates one Wigner d-Functions.
//
// Modification history:
//
//    fkw           February 2, 2001     changes to satisfy KCC
//    RYD            August 10, 2000         Module created
//
//------------------------------------------------------------------------
//
#include "EvtdFunctionSingle.hh"
#include "EvtPatches.hh"
#include <assert.h>
#include <iostream>
#include <math.h>
#include <stdlib.h>
 
EvtdFunctionSingle::EvtdFunctionSingle() {
  _j    = 0;
  _m1   = 0;
  _m2   = 0;
  _coef = 0;
  _kmin = 0;
  _kmax = 0;
}
 
EvtdFunctionSingle::~EvtdFunctionSingle() {
  if ( _coef != 0 ) delete[] _coef;
}
 
void EvtdFunctionSingle::init( int j, int m1, int m2 ) {
 
  assert( abs( m2 ) >= abs( m1 ) );
  assert( m2 >= 0 );
 
  _j  = j;
  _m1 = m1;
  _m2 = m2;
 
  _kmin = _m2 - _m1;
  _kmax = _j - _m1;
 
  assert( _kmin <= _kmax );
 
  _coef = new double[( _kmax - _kmin ) / 2 + 1];
 
  int k;
 
  for ( k = _kmin; k <= _kmax; k += 2 )
  {
    int sign = 1;
    if ( ( k - _m2 + _m1 ) % 4 != 0 ) sign = -sign;
    // fkw change to satisfy KCC
    double fkwTmp = fact( ( _j + _m2 ) / 2 ) * fact( ( _j - _m2 ) / 2 ) *
                    fact( ( _j + _m1 ) / 2 ) * fact( ( _j - _m1 ) / 2 );
    _coef[( k - _kmin ) / 2] =
        sign * sqrt( fkwTmp ) /
        ( fact( ( _j + _m2 - k ) / 2 ) * fact( k / 2 ) * fact( ( _j - _m1 - k ) / 2 ) *
          fact( ( k - _m2 + _m1 ) / 2 ) );
 
    // fkw _coef[(k-_kmin)/2]=sign*sqrt(fact((_j+_m2)/2)*fact((_j-_m2)/2)*
    // fkw          fact((_j+_m1)/2)*fact((_j-_m1)/2))/
    // fkw  (fact((_j+_m2-k)/2)*fact(k/2)*fact((_j-_m1-k)/2)*fact((k-_m2+_m1)/2));
 
    // report(INFO,"EvtGen") << "k, coef:"<<k/2<<" "<<_coef[(k-_kmin)/2]<<endl;
  }
}
 
double EvtdFunctionSingle::d( int j, int m1, int m2, double theta ) {
 
  // report(INFO,"EvtGen") << "j,m1,m2:"<<j<<","<<m1<<","<<m2<<" theta:"<<theta<<endl;
 
  assert( j == _j );
  assert( m1 == _m1 );
  assert( m2 == _m2 );
 
  double c2 = cos( 0.5 * theta );
  double s2 = sin( 0.5 * theta );
 
  double d = 0.0;
 
  int k;
  for ( k = _kmin; k <= _kmax; k += 2 )
  {
    d += _coef[( k - _kmin ) / 2] * pow( c2, ( 2 * _j - 2 * k + m2 - m1 ) / 2 ) *
         pow( s2, ( 2 * k - m2 + m1 ) / 2 );
  }
 
  return d;
}
 
int EvtdFunctionSingle::fact( int n ) {
 
  assert( n >= 0 );
 
  int f = 1;
 
  int k;
  for ( k = 2; k <= n; k++ ) f *= k;
 
  return f;
}