Iij = f (Ri, Aj)
Interaction (I) between i and j is a function of repulsive forces (R) at i and attractive forces (A) at j, and an inverse function of the friction/distance (D) between i and j
Iij The interaction volume from i to j
Ri a parameter representing (repulsive) factors which are associated with "leaving" i (such as outmigration)
Aj a parameter representing (attractive) factors related to going to j (such as inmigration)
Dij the distance between i and j
Ok Erik er...Dennis. All that does is recognize there is a force going out and potentially one coming in. It doesn't recognize how the force is being generated in, and from, i. Nor how it is either being met, changed, or redirected...within...the body of j.
Which is the heart of the matter since the results- changes everything.