Figure 2.

States are defined as directed voxel edges. For instance S_j describes particles traveling from voxel A to B, while S_i describes those moving from voxel B to C. The transition probability between these states (T_ij) is defined by integrating the product of the FOD, at the intermediate voxel (voxel B) evaluated at the acceptance angle (ω_in ∈ Ω_out) and the outgoing angle (ω_in ∈ Ω_out) and a directional coupling term (c(ω_in, Ω_out)), which penalizes large turns.