how to define udf file for for source term, scattering, absorption coefficient.
 

hello,
i am working on solar collector modeling, but I have failed to write udf file for user defined function for momentum source term, scattering, absorption coefficient.
this is the error i am getting for cords of momentum source term (structure reference not implemented)

cords:
#include "udf.h"
#include "math.h"
#define H 2
#define To 300
#define kio 0.06
#define pi 3.14

DEFINE_SOURCE(ymom_source,cell,thread,ds,eqn)
{
real x[1];
double Fk;
double beta=0.000222297;
real T=C_T(cell,thread);
double kim;
kim=kio/(1+beta*(T-To));

Fk=(2*kim*pow(H,2)*(-kio*beta)/(1+beta*pow(T-To,2))*x[1].ds[T]*x[1];
return Fk;
}