[ALEXZHUANG]

Hi, world!
I am trying to know the function of DEFINE_DPM_SOURCE in the fluent software.
The example of DEFINE_DPM_SOURCE is as following.

DEFINE_DPM_SOURCE(dpm_source, c, t, S, strength, p)
{ real mp_dot;
Material *sp = P_METERIAL(p);

/* mp_dot is the (positive) mass source to the continuous phase */
/* (Difference in mass between entry and exit from cell) */
/* multiplied by strength (Number of particles/s in stream) */
mp_dot = (P_MASS0(p) - P_MASS(p)) * strength;
C_DPMS_YI(c,t,0) += mp_dot;
/* add latent heat of vaporization to dpm energy source */
C_DPMS_ENERGY(c,t) -= mp_dot * MATERIAL_PROP(sp,PROP_latent_heat);
/* Sensible heat dealt with by Fluent Automatically */

}

I am confused about the udf. There are some questions as follows.
1. what are the meanings of mp_dot& C_DPMS_YI(c,t,0)& S->species[*_index]&strength?
2. Should mp_dot always be positive?
3. Is there any difference between C_DPMS_YI(c,t,0) and S->species[*_index] ?
4. Is strength dimensionless
5. Does C_DPMS_YI(c,t,0）only point to the gas?

Many thanks! Alex