- Steady-state equation for neutral particle collision density
:

- with

- which says that the collision density at is the
sum of
- source particles
*q*born at transported (via kernel*T*) to

where they have their first collision, - plus, particles at
colliding (via kernel
*C*) into

& transported (by*T*) to next collision at .

- source particles
- Time dependent equation can be put into same form:

- and

- where

- and .
- Only new term is initial source,
- Neutrals from initial condition (time 0) which don't have
their first collision until
*t*. - Treated in code as one additional source [Reiter, 1995],

- Neutrals from initial condition (time 0) which don't have
their first collision until

Wed Nov 26 10:29:07 EST 1997