[iitgbim]

here is part of udf, where I am getting error (not defined variable)

# include "udf.h"
# define C 0.3
# define diam2 2.e-4
# define Cmu 0.09

DEFINE_EXCHANGE_PROPERTY(modified_drag,cell,mix_th read,s_col,f_col)

{
Thread*thread_l;
Thread*thread_g;

real slip_x;
real slip_y;
real slip_z;
real slip;
real k_l;
real d_l;
real mu_t_l;
real mu_l;
real rho_l;
real rho_g;
real reyp;
real cd;

/* liquid phase-primary*/

thread_l=THREAD_SUB_THREAD(mix_thread,s_col);

/* gas phase-secondary*/

thread_g=THREAD_SUB_THREAD(mix_thread,f_col);

/* slip velocity*/

slip_x=C_U(cell,thread_l)-C_U(cell,thread_g);
slip_y=C_V(cell,thread_l)-C_U(cell,thread_g);
slip_z=C_W(cell,thread_l)-C_W(cell,thread_g);

/*Parameters*/

rho_g = C_R(cell, thread_g);
rho_l = C_R(cell, thread_l);
mu_l = C_MU_L(cell, thread_l);

/*turbulent kinetic energy and dissipation rate for liquid*/

k_l=C_K_L(cell,thread_l);
d_l=C_D_L(cell,thread_l);

It says C_D_L is not defined