Again, the objective function (14) implies minimization of all variable production costs as well as the transportation costs. The difference between the objective function (1) and (14) is in the part considering the transportation costs. Constraints (15) say that each customer's demand for each product will be satisfied. Similar to (3), constraints (16) specify that for each type of product and each plant the amount of the product shipped from the plant to all the customers cannot be greater than the quantity produced in that plant. Again, because of the inequality sign in constraints (17) the producers are not forced to operate in the whole planning period. Constraints (18) are nonnegativity constraints on variables