Diffusion Step clarification #3

Hey,
Just curious if your diffusion step is incomplete.
I'm doing a comparison of your method with another method so implementing your code and I noticed this.

In equation 18 of the paper , there are two diffusion steps ( angular and directional diffusion). In your implementation you do have a second order finite difference implemented with a incomplete gamma equation(compared to the paper) but no mention of the delta(directional diffusion) part of the equation. You also seem to be missing the groupspeed applied to advected amplitude.
I ran through your code several times and don't see these implemented. Am I missing something?

Please let me know. Thanks.