[mimi0201]

As I know, track particle information on a particular wall just hook the udf to that wall and leave others as default (reflect). I'm not sure if this is correct or not but i have met a problem. when i track particles on each wall, the total amount of particles by adding them together is not equal to which all walls are selected...it really confuses me.

[`e`]

What's your end goal?

It's a little hard to understand what you're meaning. Say you have three faces: A, B and C. Suppose you track on A and reflect on B and C then repeat this process for faces B and C. Of course the total number of tracked particles (from A, B and C individually) would be greater than if you were to track all three at once; because some particles will reflect from B and C onto A etc.