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EvtdFunctionSingle.cpp
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EvtdFunctionSingle.cpp
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/***********************************************************************
* Copyright 1998-2020 CERN for the benefit of the EvtGen authors *
* *
* This file is part of EvtGen. *
* *
* EvtGen is free software: you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation, either version 3 of the License, or *
* (at your option) any later version. *
* *
* EvtGen is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
* GNU General Public License for more details. *
* *
* You should have received a copy of the GNU General Public License *
* along with EvtGen. If not, see <https://www.gnu.org/licenses/>. *
***********************************************************************/
#include "EvtGenBase/EvtdFunctionSingle.hh"
#include "EvtGenBase/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;
double tmp = fact( ( _j + _m2 ) / 2 ) * fact( ( _j - _m2 ) / 2 ) *
fact( ( _j + _m1 ) / 2 ) * fact( ( _j - _m1 ) / 2 );
_coef[( k - _kmin ) / 2] =
sign * sqrt( tmp ) /
( fact( ( _j + _m2 - k ) / 2 ) * fact( k / 2 ) *
fact( ( _j - _m1 - k ) / 2 ) * fact( ( k - _m2 + _m1 ) / 2 ) );
}
}
double EvtdFunctionSingle::d( int j, int m1, int m2, double theta )
{
assert( j == _j );
_unused( 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;
}

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