Table 1. variables and sets used in model derivation.

Variables:
pj	Probability of using node j, also the attachment or connection probability
ϕj	Fitness of node j
Uj	Inverse fitness (or unfitness) of node j (Uj = 1/ϕj)
qj	Dual variable for node j ∈ N, which measures degree of avoidance measured on the scale 0 to 1
hr	Probability that path r ∈ R is selected
δjkr	1 if node j ∈ Nk lies on path r ∈ R and 0 otherwise (node j may lie in multiple paths)
ϕjk	Fitness of node j ∈ Nk
Ujk	Unfitness of node j ∈ Nk
V	Network unfitness
Sets:
N	Set of nodes
R	Set of all feasible paths (or supply chains), whereby all paths share a common origin and a common destination
K	Set of tiers
Nk	Set of nodes in tier k, k ∈ K