Add factors to cost function accounting for productions and attractions

[isaac-tfn]

As in a real gravity model, the 'mass' of the origin and destination should be included in a function producing demand between an O-D pair. This is currently achieved purely through furnessing but parameterising explicitly would be better.

[nhannguyen2212]

Cost function GC[i,j] = Time[i,j] ppm + Dist[i,j] ppk + Toll[i,j] + f(P[i], A[j]) or rewritten as GC[i,j] = Dist[i,j] + Time[i,j] * ppm/ppk + toll[i,j] / ppk + f(P[i], A[j])

• f(P[i], A[j]) is a function to determine "attractiveness" between origin[i] and destination[j] trip-ends
• f can be an inverse function or function that returns negative values to reflect reduced "deterrence" between origin[i] and destination[j]
• needs more investigation and tests with a few possible candidates
• example: f = -(alpha (P[i] / max(P[i])) + beta (A[j] / max(A[j]))) * Dist[i,j]