The objective function is comprised of three terms where the first
one from the left denotes the sum of fixed vehicle cost and the second
one illustrates the sum of retailer dependent material handling cost and
the third shows the sum of inventory holding cost. Equation (4) shows
that the inventory quantity in the current period for a product is equal
to the sum of the newly arrived products plus the products remaining
from the previous period minus the current demand. Equations (5)
and (6) are the variables defined formerly. Constraint (7) ensures
that the amount of delivered goods by a vehicle in a defined period
should not exceed the loading capacity of that vehicle. Constraints (8)
and (9) ensure that conditions (1) and (2) will be satisfied respectively.
Constraints (10) and (11) are related to non-negative and binary
conditions respectively.