Table 1

Table of notations

Sets
VSet of indexes for warehouses vV
TSet of indexes for periods tT
ISet of indexes for demand points iI
FSet of indexes for products fF
Parameters
λvtThe arrival rate of vehicles at the warehouse v in the period t
µvtUnloading rate at the warehouse v at period t
ρvtThe traffic intensity of queue formed warehouse v in the period t
kvWaiting rooms space for the warehouse v
SvMaximum number of servers at the warehouse v
capvfThe capacity of arrival vehicles to the warehouse v for product type f
pitfThe demand of demand point i in the period t for product type f
QvfThe capacity of distribution vehicles of the warehouse v for product type f
τilThe traveling time between demand point i and demand point l
τivThe traveling time between demand point i and warehouse v
cil Traveling cost between demand point i and l
wtiImportance of demand point i
BiUnloading time in the demand point i
ωvfInventory cost of warehouse v for product type f
Decision variables
svNumber of allocated servers to warehouse v
wvtAverage waiting time for vehicles in the warehouse v in the period t
wqvtAverage waiting time for vehicles in the queues in the warehouse v in the period t
LvtThe average number of vehicles in the warehouse v in the period t
LqvtThe average number of vehicles in the queues in the warehouse v in the period t
πnvtProbability of existence of n vehicles in the warehouse v in the period t
IvtfInventory level of product f in the warehouse v at the end of the period t
zivtIf demand point i is assigned to warehouse v in the period t 1, otherwise 0
x0ivtIf demand point i is the first demand point in any route of warehouse v in the period t
xilvtIf demand point i is visited just after demand point i in any route of warehouse v in the period t
xi0vtIf demand point i is the last demand point in any route of warehouse v in the period t
utifA continuous variable which represents the load of the vehicle after visiting demand point i in the period t
rivtResponse time to the demand point i in the period t if it is allocated to the warehouse v

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