A Hybrid Approach to the Optimization of Multiechelon Systems

Table 2

Summary indices, parameters, and decision variables.

Symbol	Description
Indices
	Number of satellites
	Number of customers
	Deport
	Set of satellites
	Set of customers
Parameters
	Number of the 1st-level vehicles
	Number of the 2nd-level vehicles
	Capacity of the vehicles for the 1st level
	Capacity of the vehicles for the 2nd level
	Demand required by customer
	Cost of the arc()
	Cost of loading/unloading operations of a unit of freight in satellite
Decision variables
	An integer variable of the 1st-level routing is equal to the number of 1st-level vehicles using arc()
	A binary variable of the 2nd-level routing is equal to 1 if a 2nd-level vehicle makes a route start from satellite and go from node to node and 0 otherwise
	The freight flow arc() for the first level
	The freight arc() where represents the satellite where the freight is passing through.
	A binary variable that is equal to 1 if the freight to be delivered to customer is consolidated in satellite and 0 otherwise