(fitteia's extended models library)
double RNordio(double f, double S, double A0, double A1, double A2, double Dz, double Dx)
{
double JRotNordio_();
double y;
double J1;
double J2;
double w;
/** eq. 7.61 Dong's Book 2nd ed **/
/** beta(mL,mM) from A131 Supporting Info or Fig. 7.1 Dong's Book **/
/** c(mL,mM) instead of k(mL,mM), Dong's Book eq. 7.61 and 1988-JCP88pp1443 **/
w=2*pi*f;
J1=JRotNordio_(1,w,S,A0,A1,A2,Dz,Dx);
J2=JRotNordio_(2,w,S,A0,A1,A2,Dz,Dx);
y=Arot*(J1+J2);
// printf("Relax_rate = %le", y);
return y;
}