Since I cannot find a odd c++ code ( < c++11 ) for the calculation of those j-symbol, I made one for myself!

The code just using the formula which you can find in wiki or here. So, the code is not optimized, but for simple calculation, I guess it does not matter. Also, I checked, in my pc, calculate 1000 9-j symbols only take 1 or 2 sec.

The program first build

1. factorial
2. Clebsch–Gordan coefficient
3. 3-j symbol
4. 6-j symbol
5. 9-j symbol

This is not a good place (or I don’t know how to) for code display…. any way.

```#include <stdlib.h>
#include <cmath>

double factorial(double n){
if( n < 0 ) return -100.;

return (n == 1. || n == 0.) ? 1. : factorial(n-1) * n ;
}

double CGcoeff(double J, double m, double J1, double m1, double J2, double m2){
// (J1,m1) + (J2, m2) = (J, m)

if( m != m1 + m2 ) return 0;

double Jmin = abs(J1 - J2);
double Jmax = J1+J2;

if( J < Jmin || Jmax < J ) return 0;

double s0 = (2*J+1.) * factorial(J+J1-J2) * factorial(J-J1+J2) * factorial(J1+J2-J) / factorial(J+J1+J2 + 1.);
s0 = sqrt(s0);

double s = factorial(J +m ) * factorial(J -m);
double s1 = factorial(J1+m1) * factorial(J1-m1);
double s2 = factorial(J2+m2) * factorial(J2-m2);
s = sqrt(s * s1 * s2);

//printf(" s0, s = %f , %f \n", s0, s);

int kMax = min( min( J1+J2-J, J1 - m1), J2 + m2);

double CG = 0.;
for( int k = 0; k <= kMax; k++){
double k1 = factorial(J1+J2-J-k);
double k2 = factorial(J1-m1-k);
double k3 = factorial(J2+m2-k);
double k4 = factorial(J - J2 + m1 +k);
double k5 = factorial(J - J1 - m2 +k);
double temp = pow(-1, k) / (factorial(k) * k1 * k2 * k3 * k4 * k5);
if( k1 == -100. || k2 == -100. || k3 == -100. || k4 == -100. || k5 == -100. ) temp = 0.;

//printf(" %d | %f \n", k, temp);
CG += temp;
}

return s0*s*CG;

}

double ThreeJSymbol(double J1, double m1, double J2, double m2, double J3, double m3){

// ( J1 J2 J3 ) = (-1)^(J1-J2 - m3)/ sqrt(2*J3+1) * CGcoeff(J3, -m3, J1, m1, J2, m2)
// ( m1 m2 m3 )

return pow(-1, J1 - J2 - m3)/sqrt(2*J3+1) * CGcoeff(J3, -m3, J1, m1, J2, m2);

}

double SixJSymbol(double J1, double J2, double J3, double J4, double J5, double J6){

// coupling of j1, j2, j3 to J-J1
// J1 = j1
// J2 = j2
// J3 = j12 = j1 + j2
// J4 = j3
// J5 = J = j1 + j2 + j3
// J6 = j23 = j2 + j3

//check triangle condition
if( J3 < abs(J1 - J2 ) || J1 + J2 < J3 ) return 0;
if( J6 < abs(J2 - J4 ) || J2 + J4 < J6 ) return 0;
if( J5 < abs(J1 - J6 ) || J1 + J6 < J5 ) return 0;
if( J5 < abs(J3 - J4 ) || J3 + J4 < J5 ) return 0;

double sixJ = 0;

for( float m1 = -J1; m1 <= J1 ; m1 = m1 + 1){
for( float m2 = -J2; m2 <= J2 ; m2 = m2 + 1){
for( float m3 = -J3; m3 <= J3 ; m3 = m3 + 1){
for( float m4 = -J4; m4 <= J4 ; m4 = m4 + 1){
for( float m5 = -J5; m5 <= J5 ; m5 = m5 + 1){
for( float m6 = -J6; m6 <= J6 ; m6 = m6 + 1){

double f = (J1 - m1) + (J2 - m2) + (J3 - m3) + (J4 - m4) + (J5 - m5) + (J6 - m6);

double a1 = ThreeJSymbol( J1, -m1, J2, -m2, J3, -m3); // J3 = j12
double a2 = ThreeJSymbol( J1, m1, J5, -m5, J6, m6); // J5 = j1 + (J6 = j23)
double a3 = ThreeJSymbol( J4, m4, J2, m2, J6, -m6); // J6 = j23
double a4 = ThreeJSymbol( J4, -m4, J5, m5, J3, m3); // J5 = j3 + j12

double a = a1 * a2 * a3 * a4;
//if( a != 0 ) printf("%4.1f %4.1f %4.1f %4.1f %4.1f %4.1f | %f \n", m1, m2, m3, m4, m5, m6, a);

sixJ += pow(-1, f) * a1 * a2 * a3 * a4;

}
}
}
}
}
}

return sixJ;
}

double NineJSymbol( double J1, double J2, double J3, double J4, double J5, double J6, double J7, double J8, double J9){

double gMin = min( min (min( abs(J1 - J2 ), abs(J4 - J5)) , abs( J4 - J6 )) , abs(J7 - J8));
double gMax = max( max (max( J1+J2, J4+J5), J3+J6), J7+J8);

//printf(" gMin, gMax = %f %f \n", gMin, gMax);

double nineJ = 0;
for( float g = gMin; g <= gMax ; g = g + 1){
double f = pow(-1, 2*g) * (2*g+1);
double s1 = SixJSymbol(J1, J4, J7, J8, J9, g);
if( s1 == 0 ) continue;
double s2 = SixJSymbol(J2, J5, J8, J4, g, J6);
if( s2 == 0 ) continue;
double s3 = SixJSymbol(J3, J6, J9, g, J1, J2);
if( s3 == 0 ) continue;
nineJ += f* s1*s2*s3;
}

return nineJ;
}```