Directional diffusion tensor generation


I’m looking into generating directional diffusion tensor group constants for a neutron diffusion code to calculate neutron flux in optically thin media (e.g. air). In particular, this publication by Trahan & Larsen introduces one method for generating the diffusion tensor by evaluating the following integral from Eq 13:
where f_1 is the angular neutron flux solution of a purely absorbing, fixed source problem. Would this be a challenging task? I’ve looked through the documentation and python API source code about filters and scores, but I haven’t been able to figure it out myself.

On a side note, I saw the publication and discussion about the CMM method, but unfortunately it would not work for my cases because I cannot homogenize across the whole universe.